GIFT  TO  THE  LIBRARY 

CIVIL  ENGINEERING  DEPARTMENT 

UNIVERSITY  OF  CALIFORNIA 

BY 

PROFESSOR  FRANK  SOULE 
1912 


L- 


WORKS  OF  PROF.  S.  E.  TILLMAN 


PUBLISHED    BY 


JOHN   WILEY   &   SONS, 


Descriptive  General  Chemistry. 

A    Text-book    for    Short    Course.      8vo,    cloth, 
83.00,  net. 

Elementary   Lessons  in   Heat. 

Second    edition,    revised    and    enlarged.       8vo, 
cloth,  $1.50,  net. 

A  Text-book  of  Important  Minerals  and  Rocks. 

With  Tables  for  the  Determination  of  Minerals. 
8vo,  cloth,  186  pages.     $2.00,  net. 


A  TEXT-BOOK     . 


OF 


IMPORTANT  MINERALS 
AND  ROCKS. 


WITH 

TABLES  FOR    THE  DETERMINATION 
OF  MINERALS. 


BY 


S.    E.    TILLMAN, 

of  Chemistry \  Mineralogy,  ant 
U.  S.  Military  Academy,  West  Point,  N.  Y. 


Professor  of  Chemistry,  Mineralogy,  and  Geology, 


FIRST  EDITION. 
FIRST    THOUSAND. 


NEW  YORK: 

JOHN  WILEY  &  SONS. 

LONDON:   CHAPMAN  &   HALL,   LIMITED. 

1900. 


'  -•*  V:  X-  "">  "•  - 


Copyright,  1900, 

BY 
S.  E.  TILLMAN, 


ROBERT  DRUMMOND,   PRINTER,   NEW  YORK. 


PREFACE. 


THIS  book  is  the  slow  outgrowth  of  the  efforts  to  meet 
the  necessities  of  this  institution  for  a  convenient  text-book 
of  the  important  minerals  and  rocks.  The  number  of  min- 
eral species  has  reached  nearly  one  thousand  and  is  con- 
stantly increasing.  Of  this  number  less  than  one-tenth  is  of 
common  occurrence  or  can  be  considered  of  much  economic 
importance,  and  a  small  proportion  of  this  same  tenth  in- 
cludes the  essential  constituents  of  all  roeks.  To  embrace 
in  descriptive  text  all  mineral  species  necessarily  results  in 
an  embarrassing  mass  of  matter  for  the  general  student. 
Similar  embarrassment,  though  to  a  less  extent,  is  experienced 
in  complete  descriptions  of  all  the  rocks/  To  reduce  these 
descriptions  to  a  convenient  yet  satisfactory  form  for  gen- 
eral students  is  the  object  of  the  present  effort. 

There  are  described  in  the  book  about  seventy-five  dis- 
tinct species  of  the  important  and  in  the  main  common  min- 
erals, and  the  principal  members  of  the  different  classes  of 
rocks.  It  is  thought  that  the  selection  is  extended  enough 
for  general  purposes,  and  it  includes  abundant  material  for 
the  study  of  both  minerals  and  rocks.  The  book  is  prima- 
rily prepared  to  meet  the  necessities  of  the  Military  Academy, 
whose  students  are  well  fitted  for  the  work  when  they  begin 
it,  have  excellent  opportunity  for  the  examination  and  com- 
parison of  specimens,  and  for  laboratory  work  in  determin- 

iii 


785375 


IV  PREFACE. 

ing  them.  It  is  hoped  that  the  book  may  be  of  conveni- 
ence to  a  larger  class  of  students  whose  facilities  in  the 
study  may  be  less,  but  whose  aim  is  the  same  as  ours — to 
acquire  a  fair  knowledge  of  the  important  minerals  and 
rocks. 

Chapter  I  of  the  book  contains  in  brief  outline  the  more 
fundamental  principles  of  crystallography,  followed  by  a 
description  of  the  different  crystalline  systems  and  of  some 
of  the  more  important  crystalline  aggregates  and  irregular 
forms.  The  subject-matter  of  the  chapter  can  be  almost 
indefinitely  extended  by  lecture  if  so  desired.  The  reason 
that  the  crystallographic  branch  is  so  briefly  treated  is  stated 
in  the  introduction  to  the  book,  no  other  treatment  being 
considered  appropriate  in  a  short  general  course. 

Chapter  II  contains  a  short  description  of  the  general 
properties  of  minerals,  of  the  laboratory  facilities  for  de- 
termining them,  and  of  the  manner  of  using  these  facilities. 

In  Chapter  III  an  effort  has  been  made  to  give  a  concise 
and  accurate  statement  of  the  more  readily  observed  phy- 
sical properties  of  the  mineral  species  and  of  the  ordinary 
mineralogical  tests  for  distinguishing  and  determining  them. 
There  are  also  added  many  desirable  facts  relating  to  the 
use  and  occurrence  of  the  minerals. 

A  table  for  the  determination  of  minerals  follows  this 
chapter  and  is  intended  for  a  guide  and  companion  in  the 
practical  examinations  and  tests  of  the  minerals. 

The  table  merely  puts  in  condensed  form  the  described 
properties  and  characteristics  of  the  minerals  as  given  in 
Chapter  III.  This  tabular  arrangement  has  many  advan- 
tages over  a  descriptive  text-book  without  tables,  or  with 
tables  bound  in  separate  form.  A  statement  of  the  proper- 
ties of  each  species  in  the  body  of  the  text  as  well  as  in  the 
table  has  been  found  advantageous  when  recitation  and 
practical  work  are  conducted  simultaneously. 

The  tables  have  been  a  slow  growth,  of  nearly  twenty 
years,  from  very  simple  beginnings,  and  have  during  that 
time  been  used  by  our  pupils  under  separate  binding.  In 


PREFA  CE.  -      V 

this  preparation  I  have  had  valuable  suggestions  from  sev- 
eral officers  who  have  served  as  instructors  in  the  depart- 
ment, but  I  would  here  especially  acknowledge  my  great 
indebtedness  to  Capt.  J.  P.  Wisser,  /th  U.  S.  Artillery,  who, 
as  Lieutenant  Wisser  and  while  serving  as  Assistant  Profes- 
sor in  the  Department  in  1890  and  '91,  did  the  larger  part  of 
the  work  which  placed  the  tables  in  their  present  shape. 

Part  II  is  devoted  to  the  common  rocks.  The  prin- 
ciples of  classification,  the  classes,  and  the  distinguishing 
characteristics  of  each  class  are  given ;  the  appearance  of  the 
different  members  of  each  class  is  described  and  their  min- 
eral composition  given,  to  which  are  added  many  important 
facts  as  to  occurrence  and  use  and  the  more  prominent  con- 
clusions as  to  origin. 

The  greater  portion  of  the  matter  contained  in  the 
book,  exclusive  of  the  mineral  tables  and  the  contents  of 
Chapter  I,  has  been  used  at  the  Academy  for  the  past  six 
years,  and  has  been  frequently  added  to  and  revised  during 
that  time. 

The  arrangement  of  mineral  species  in  the  text  is  mod- 
eled after  that  of  the  late  Professor  J.  DrDana  in  his  man- 
ual of  Mineralogy  and  Petrography.  The  mineral  com- 
pounds of  the  same  metals  are  brought  together,  except  in 
the  case  of  silicates.  The  important  metals  and  their  ores 
are  consecutively  treated,  as  are  the  important  rock-making 
minerals.  This  arrangement  has,  from  experience,  been 
found  very  satisfactory. 

In  the  preparation  of  this  little  book  I  have  consulted 
many  authorities,  but  would  especially  acknowledge  my 
obligations  for  mineralogical  matter  to  the  works  of  Pro- 
fessors J.  D.  Dana,  E.  S.  Dana,  G.  J.  Brush,  S.  L.  Penfield, 
H.  Bauerman,  W.  O.  Crosby,  D.  M.  Barringer ;  for  petro- 
graphic  material  to  various  published  papers  of  the  U.  S. 
Geological  Survey,  to  the  works  of  Professors  J.  F.  Kemp, 
W.  B.  Scott,  and  J.  D.  Dana;  for  the  chapter  on  Crystal- 
lography to  the  works  of  Professors  G.  H.  Williams,  E.  S» 
Dana,  H.  Bauerman,  and  N.  Story  Maskelyne. 


of  the  more  important  crystalline  aggregates  cj 
forms.     The  subject-matter  of  the  chapter  a 
indefinitely  extended  by  lecture  if  so  desired, 
that  the  crystallographic  branch  is  so  briefly  trej 
in  the  introduction  to  the  book,  no  other  tre; 
considered  appropriate  in  a  short  general  courj| 

Chapter  II  contains  a  short  description  o™JBp"c 
properties  of  minerals,  of  the  laboratory  facil™ 
termining  them,  and  of  the  manner  of  using  th| 

In  Chapter  III  an  effort  has  been  made  to  gj 
and  accurate  statement  of  the  more  readily  oti 
sical  properties  of  the  mineral  species  and  of  • 
mineralogical  tests  for  distinguishing  and  deter™ 
There  are  also  added  many  desirable  facts  re| 
use  and  occurrence  of  the  minerals. 

A  table  for  the  determination  of  minerals 
chapter  and  is  intended  for  a  guide  and  comp 
practical  examinations  and  tests  of  the  minerals 

The  table  merely  puts  in  condensed  form  t 
properties  and  characteristics  of  the  minerals  'Wrcii  til 
Chapter  III.  This  tabular  arrangement  has  many  advan- 
tages over  a  descriptive  text-book  without  tables,  or  with 
tables  bound  in  separate  form.  A  statement  of  the  proper- 
ties of  each  species  in  the  body  of  the  text  as  well  as  in  the 
table  has  been  found  advantageous  when  recitation  and 
practical  work  are  conducted  simultaneously. 

The  tables  have  been  a  slow  growth,  of  nearly  twenty 
years,  from  very  simple  beginnings,  and  have  during  that 
time  been  used  by  our  pupils  under  separate  binding.  In 


PREFA  CE.  •       V 

this  preparation  I  have  had  valuable  suggestions  from  sev- 
eral officers  who  have  served  as  instructors  in  the  depart- 
ment, but  I  would  here  especially  acknowledge  my  great 
indebtedness  to  Capt.  J.  P.  XVisser,  /th  U.  S.  Artillery,  who, 
as  Lieutenant  Wisser  and  while  serving  as  Assistant  Profes- 
sor in  the  Department  in  1890  and  '91,  did  the  larger  part  of 
the  work  which  placed  the  tables  in  their  present  shape. 

Part  II  is  devoted  to  the  common  rocks.  The  prin- 
ciples of  classification,  the  classes,  and  the  distinguishing 
characteristics  of  each  class  are  given  ;  the  appearance  of  the 
different  members  of  each  class  is  described  and  their  min- 
eral composition  given,  to  which  are  added  many  important 
facts  as  to  occurrence  and  use  and  the  more  prominent  con- 
clusions as  to  origin. 

The  greater  portion  of  the  matter  contained  in  the 
book,  exclusive  of  the  mineral  tables  and  the  contents  of 
Chapter  I,  has  been  used  at  the  Academy  for  the  past  six 
years,  and  has  been  frequently  added  to  and  revised  during 
that  time. 

The  arrangement  of  mineral  species  in  the  text  is  mod- 
eled after  that  of  the  late  Professor  J.  DrDana  in  his  man- 
ual of  Mineralogy  and  Petrography.  The  mineral  com- 
pounds of  the  same  metals  are  brought  together,  except  in 
the  case  of  silicates.  The  important  metals  and  their  ores 
are  consecutively  treated,  as  are  the  important  rock-making 
minerals.  This  arrangement  has,  from  experience,  been 
found  very  satisfactory. 

In  the  preparation  of  this  little  book  I  have  consulted 
many  authorities,  but  would  especially  acknowledge  my 
obligations  for  mineralogical  matter  to  the  works  of  Pro- 
fessors J.  D.  Dana,  E.  S.  Dana,  G.  J.  Brush,  S.  L.  Penfield, 
H.  Bauerman,  W.  O.  Crosby,  D.  M.  Barringer ;  for  petro- 
graphic  material  to  various  published  papers  of  the  U.  S. 
Geological  Survey,  to  the  works  of  Professors  J.  F.  Kemp, 
W.  B.  Scott,  and  J.  D.  Dana;  for  the  chapter  on  Crystal- 
lography to  the  works  of  Professors  G.  H.  Williams,  E.  S. 
Dana,  H.  Bauerman,  and  N.  Story  Maskelyne. 


VI  PREFACE. 

Through  the  courtesy  of  Professor  E.  S.  Dana  I  have 
been  permitted  to  use  the  crystalline  figures  shown  under 
numbers  2,  3,  4,  $,  18,  20,  22,  25,  and  26,  which  are  taken 
from  his  Text-book  of  Mineralogy.  Figures  19,  31,  32,  33, 
and  34  are  from  Williams's  Elements  of  Crystallography, 
through  the  courtesy  of  the  publishers,  Henry  Holt  &  Co. 

S.  E.  TILLMAN, 

U.  S.  MILITARY  ACADEMY,  WEST  POINT,  N.  Y., 
October  i,  1900. 


TABLE  OF  CONTENTS. 


PART  I. 
IMPORTANT  MINERALS. 

CHAPTER  I. 

ELEMENTS  OF  CRYSTALLOGRAPHY. 

PAGES 

INTRODUCTORY  REMARKS 1-3 

GEOMETRIC  SYMMETRY 3-4 

CRYSTALLOGRAPHIC  SYMMETRY ~. 4-6 

CRYSTALLOGRAPHIC  AXES 6-9 

CRYSTALLOGRAPHIC  LAWS 9-10 

CRYSTALLINE  SYSTEMS 11-18 

CRYSTAL  FORMS 18 

DISTORTIONS  IN  CRYSTALS 19-22 

CRYSTALLINE  AGGREGATES 23-24 

CHAPTER  II. 

PHYSICAL  AND  CHEMICAL  PROPERTIES  OF  MINERALS. 

PHYSICAL  PROPERTIES  OF  MINERALS 25-27 

•CHEMICAL  PROPERTIES  OF  MINERALS 27-31 

CHAPTER  III. 

DESCRIPTIVE  MINERALOGY. 

NATIVE  ELEMENTS 32-40 

ORES  OF   SILVER 40-42 

ORE  OF  MERCURY  42-43 

COPPER  AND  ITS  ORES 43-48 

ORES  OF  LEAD.   48-  r 

vti 


Vlll  TABLE   OF  CONTENTS. 

PAGES 

ORES  OF  ZINC 51-52 

ORES  OF  IRON 53-60 

ORES  OF  ANTIMONY  AND  MANGANESE 60-61 

TIN  ORE 61 

RARE  MINERALS 62-65 

COMPOUNDS  OF  SODIUM  AND  POTASSIUM 65-67 

COMPOUNDS  OF  CALCIUM 67-74 

QUARTZ,  SILICA 74-78 

SILICATES 78-94 

M  i  NERAL  COAL 94-96 

DESCRIPTION  OF  TABLES 96-97 

TABLES  FOR  DETERMINATION  OF  MINERALS 98-137 

PART  II. 

COMMON  ROCKS. 

ROCK  CONSTITUENTS 139-140 

CLASSIFICATION  OF  ROCKS 140-141 

SEDIMENTARY  ROCKS 141-152 

IGNEOUS  OR  UNSTRATIFIED  ROCKS 152-158 

TABULAR  CLASSIFICATION  OF  ROCKS 158 

METAMORPHIC  ROCKS 159-161 


The  following  abbreviations  are  used  in  the  text : 

Before  blowpipe B.B. 

Color C. 

Hardness H. 

Luster L. 

Oxidizing  Flame , O.F. 

Reducing  Flame .^, . .  R.F. 

Sign  of  inequality — greater  than > 

Specific  gravity G. 


PART   I. 
IMPORTANT   MINERALS. 


CHAPTER   I. 
INTRODUCTORY   REMARKS. 

THE  natural  objects  of  the  universe  can  in  general  be 
included  in  two  great  groups  or  kingdoms,  the  organic  and 
the  inorganic.  To  the  first  belong  the  bodies  which  origi- 
nate through  the  agency  of  life,  to  the  second  the  bodies  not 
thus  originating. 

Those  bodies  occurring  in  the  inorganic  kingdom  which 
have  a  definite  chemical  composition  are  termed  minerals. 
Mineralogy  is  the  science  which  describes  and  teaches  how 
to  distinguish  and  determine  minerals.  The  distinction  of 
minerals  from  each  other  is  based  upon  the  consideration  of 
the  composition,  external  form,  and  internal  structure,  all  of 
which  must  be  determined  and  investigated  in  the  full 
classification  of  minerals. 

The  term  '  mineral  species '  is  generally  made  to  include 
all  those  minerals  which  have  the  same  composition  and  a 
definite  form  and  structure.  With  few  exceptions  minerals 
at  ordinary  temperatures  are  solids,  and  all  minerals  in  be- 
coming solid,  whether  from  state  of  vapor,  fusion,  or  solu- 
tion, tend,  under  favorable  conditions,  to  form  regular 
geometrical  solids  bounded  by  plane  surfaces.  The  regular 
forms  thus  assumed  by  minerals  are  called  crystals.  The 
natural  bounding-plane  surfaces  of  a  crystal  are  called  the 
faces,  the  lines  in  which  the  faces  intersect  are  called  edges, 


CR  1  'S  TA  LLOGRA  PH  Y. 


the  angles  between  edges  are  plane  angles,  those  between 
faces  are  interfacial  angles,  and  those  formed  by  the  meeting 
of  three  or  more  faces  are  solid  angles. 

In  the  study  of  crystal  forms  it  was  early  observed — 

i st.  That  there  was  a  marked  symmetry  in  the  arrange- 
ment of  their  parts,  as  faces,  edges,  points,  etc. 

2d.  It  was  discovered  that  the  forms  of  the  same  species 
obeyed  certain  laws  that  made  possible  a  geometrical  classi- 
fication of  the  crystals  of  different  species. 

It  was  later  developed  by  studying  the  physical  proper- 
ties of  the  crystals  that  there  is  an  intimate  and  complete 
accord  between  these  properties  and  the  forms  of  the  crys- 
tals, and  that  the  form  is  but  the  obvious  external  evidence 
of  a  definite  internal  structure ;  that  it  is  the  structure  that 
is  characteristic,  the  form  and  physical  properties  are  the 
evidences  of  the  structure. 

The  consideration  of  the  properties  or  characteristics 
which  distinguish  minerals  (structure,  form,  composition) 
give  rise  to  two  distinct  divisions  of  the  science  of  min- 
eralogy. 

I.  Crystallographic   mineralogy,    which    considers    the 
form   and   structure   of   the   minerals,   and    this    has    two 
branches : 

(a)  Geometric  or  morphological  crystallography,  which 
considers  the  external  form  of  minerals  and  the  geometric 
relations  of  their  faces  and  plane  surfaces. 

(b)  Physical    crystallography,    which    investigates    the 
properties  which  are  mainly  the  result  of  structure,  i.e., 
physical   properties,  such   as   cohesion,  elasticity,  and  the 
properties  displayed  under  the  action  of  light,  heat,  elec- 
tricity, etc. 

II.  Chemical  mineralogy,  which  is  primarily  concerned 
with  determining  the  chemical  composition  of  the  minerals. 
It  also  extends  to  the  consideration  of  the  chemical  relations 
between  constitution  and  form. 

The  knowledge  obtained  through  all  the  above  branches 
of  mineralogy  when  systematically  arranged  and  presented, 
together  with  information  as  to  mode  of  occurrence,  distri- 


ELEMENTS   OF  GEOMETRIC  SYMMETRY.  3 

bution,  and  association  of  the  different  species,  constitutes 
Descriptive  Mineralogy. 

Thorough  acquaintance  with  all  branches  of  mineralogy 
are  essential  to  the  work  of  specialists,  but  for  the  general 
student  the  essentially  chemical  branch  is  far  more  impor- 
tant, for  through  it  the  composition  can  usually  be  more 
readily  determined,  and  it  is  upon  the  composition  that  all 
other  relations  depend.  For  this  reason  only  brief  reference 
will  be  made  in  this  book  to  the  crystallographic  branch, 
and  then  only  to  the  most  fundamental  principles. 

CRYSTALLOGRAPHIC   CONSIDERATIONS. 

Elements  of  Geometric  Symmetry  in  the  Form  of  Solids. — 

The  symmetry  of  form  in  solids  may  be  considered  with 
reference  to  planes  of  symmetry,  axes  of  symmetry,  or  cen- 
ters of  symmetry. 

Planes  of  Symmetry. — The  form  of  a  solid  is  geometri- 
cally symmetrical  with  reference  to  a  plane  when  the  plane 
divides  the  solid  into  two  precisely  corresponding  parts,  so 
that  every  normal  to  the  plane  section  would  meet  a  cor- 
responding point  of  the  solid  at  the  same  distance  from  the 
section.  A  polyhedron  placed  upon  a  plane  mirror  forms 
with  its  image  a  symmetrical  figure,  of  which  the  mirror 
surface  is  the  plane  of  symmetry.  Again,  a  plane  passing 
through  the  center  of  a  cube  parallel  to  either  face  divides 
it  symmetrically,  and  it  is  at  once  evident  that  there  are 
three  such  planes  for  a  cube.  So  the  planes  passing  through 
the  diagonally  opposite  edges  of  a  cube  are  planes  of  sym- 
metry. There  is  generally  a  distinction  between  the  mineral- 
ogical  symmetry  of  crystals  and  the  full  geometric  sym- 
metry of  figure  here  defined.  This  distinction  will  appear 
subsequently. 

Axes  of  Symmetry. — An  axis  of  symmetry  of  a  solid  is  a. 
line  about  which  if  the  body  be  rotated  it  will  successively 
occupy  the  same  position,  or  will  fill  the  same  place  in  space.. 
Axes  of  symmetry  can  be  distinguished  from  each  other  by 
the  number  of  times  the  body  occupies  the  same  position^ 
during  a  complete  revolution  about  each. 


CR  YS  TA  LL  OCR  A  PH  Y. 


A  cube  turned  about  a  line  joining  the  middle  point  of 
opposite  faces  will  occupy  the  same  position  four  times  dur- 
ing one  revolution  ;  such  line  is  an  axis 
of  quaternary  or  tetragonal  symmetry. 
A  line  joining  the  middle  points  of 
diagonally  opposite  edges  in  a  cube  is 
an  axis  of  binary  symmetry.  In  the 
square  octahedron,  Fig.  I,  the  vertical 
axis  a  is  an  axis  of  quaternary  sym- 
metry, while  c  and  d  are  axes  of  binary 
symmetry.  The  axis  about  which  the 
third  or  a  higher  order  exists  is  a 
principal  axis  of  symmetry;  other  axes 
are  secondary  axes. 


FIG.  i, 


Center  of  Symmetry. — A  center  of  symmetry 
of  a  solid  exists  when  a  line  passing  through  the 
center  meets  similar  points  in  the  opposite  halves  of  the  crystal  at  the 
same  distance  from  the  center.  A  center  of  symmetry  may  exist  without 
•either  axes  or  planes  of  symmetry  being  present. 

In  every  case  of  a  center  the  crystal  polyhedron  is  bounded  by  pairs 
of  parallel  planes  which  are  at  equal  distances  from  the  center,  and  it 
can  always  be  shown  that  the  points  in  which  a  line  through  the  center 
pierces  any  two  of  these  planes  are  corresponding  points  in  two  halves 
into  which  the  crystal  may  be  divided. 

Crystallographic  Symmetry. — Geometric  symmetry,  above 
referred  to,  relates  to  the  external  form  of  the  solid.  In 
crystals,  as  already  stated,  the  physical  properties  have  a 
definite,  constant  and  most  intimate  connection  with  the  ex- 
ternal form.  Both  form  and  physical  properties  are  deter- 
mined by  the  structure  of  the  particular  body ;  the  struc- 
ture is  the  most  essential  physical  character  of  the  crystal, 
and  the  form  is  only  the  most  important  external  mani- 
festation of  the  structure.  A  solid  in  the  form  of  a 
crystal,  without  the  related  internal  structure,  does  not 
constitute  a  crystal ;  such  a  solid  is  only  a  model  of  the  ex- 
ternal form. 

Natural  crystals  very  frequently  exhibit  geometric  sym- 


CR  YS TA LLOGRA PHIC  S  YMME TR  Y. 


metry  in  their  external  form,  and  it  is  thought  that  if  crys- 
tallization took  place  without  any  disturbance  of,  or  inter- 
ference with,  the  most  favorable  circumstances  for  the 
process,  geometric  symmetry  of  form  would  generally 
result.  In  such  cases  crystallographic  symmetry  would  be 
denned  by  the  relations  of  geometric  symmetry  which  would 
result.  Crystallographic  symmetry,  however,  exists  with- 
out being  completely  expressed  in  the  external  form.  The 
form  is  but  one  indication  of  the  internal  structure,  the 
physical  properties  are  another.  The  physical  character  of 
minerals  have  been  very  carefully  studied,  and  in  general 
are  found  to  be  the  same  in  all  parallel  directions.  This 
fact  is  believed  to  demonstrate  a  like  internal  structure  or 
molecular  arrangement  in  these  parallel  directions.  The 
intimate  relations  between  the  physical  character  and  the 
faces  and  planes  of  a  crystal  lead  to  the  conclusion  that  the 
planes  are  but  external  expressions  of  the  internal  structure. 
The  faces  are  accordingly  definitive  because  of  their  direc- 
tion or  angular  position,  and  not  because  of  their  size  or 
distance  from  any  assumed  origin.  Thus  Figs.  2  and  3  are 


FIG.  2. 


FIG.  3. 


equally  symmetrical  about  a  vertical  or  horizontal  plane 
passing  through  their  centers.  Again,  a  crystal  may  be  a 
crystallographic  cube,  though  departing  widely  from  the 
geometric  form,  as  in  Figs.  4  and  5,  provided  it  can  be 
shown  that  the  three  pairs  of  faces  are  alike ;  this  would 
have  to  be  done  from  the  physical  character  of  the  faces,  by 
the  kind  of  cleavage,  or  by  optical  means. 

The  important  point  to  be  grasped  in  regard  to  crystal- 
lographic symmetry  is  that  the  symmetry  in  crystals  about 


CR  YS TALLOGRAPHY. 


FIG.  4. 


FIG.  5. 


lines  or  planes  is  one  of  direction  and  not  of  position.  In 
consequence  of  this  fact  any  plane  of  a  crystal  may  be  con- 
sidered as  shifted  parallel  to  itself  without  affecting  the 
crystallographic  symmetry :  hence 
the  corresponding  symmetrical  faces 
of  a  crystal  may  be  of  very  unequal 
size  and  distance  from  the  origin, 
without  disturbing  the  crystallograph- 
ic symmetry.  In  general,  for  conven- 
ience in  the  discussion  and  description 
of  forms  it  is  better  to  consider 
symmetry  of  position  as  well  as  of 
direction  ;  in  other  words,  we  may 
readily  imagine  the  similar  crystal 
planes  to  be  shifted  in  directions  parallel  to  themselves 
until  a  solid  of  geometric  symmetry  is  produced. 

Coordinate  or  Crystallographic  Axes. — For  studying  and 
classifying  crystal  forms,  and  for  describing  the  position  of 
their  faces,  it  is  convenient  to  assume  a  system  of  coordinate 
axes  after  the  manner  of  analytical  geometry.  Different 
sets  of  axes  may,  for  this  purpose,  be  assumed  in  crystals, 
but  that  set  is  usually  employed  which  enables  expression  in 
the  simplest  manner  of  the  position  of  the  faces  and  the  re- 
lations between  different  crystalline  forms.  These  consid- 
erations have  led  to  the  selection  of  the  axes  of  symmetry  as 
coordinate  axes  whenever  the  proper  number  of  these  axes 
are  present.  If  only  one  axis  of  symmetry  is  present,  it  is 
employed  in  connection  with  two  other  assumed  directions. 
The  axes  chosen  under  the  above  conditions  will  differ  in 
their  relations  to  each  other  in  different  crystalline  forms. 
They  may  intersect  at  right  angles,  giving  orthometric  forms, 
or  obliquely,  giving  clinometric  forms.  They  may  be  all 
equal  in  length,  only  two  equal,  or  all  unequal ;  in  some 
cases  they  connect  the  centers  of  opposite  faces,  in  others 
the  middle  points  of  opposite  edges,  or  the  apices  of  oppo- 
site solid  angles.  It  should  be  remembered  that  the  axes 
usually  assumed  are  not  the  only  ones  that  could  be  em- 
ployed, but  are  such  as  afford  the  simplest  relations  for  the 


LOCATION  OF  PLANES  BY  REFERENCE    TO   AXES.          7 

descriptions  of  forms.  The  planes  in  which  the  coordinate 
axes  lie  are  called  the  axial  or  diametric  planes.  They  cor- 
respond  to  the  coordinate  planes  of  analytical  geometry, 
and  divide  the  spaces  within  the  crystal  into  eight  solid 
angles,  and  in  one  system  where  four  axes  are  used  the 
space  is  divided  into  twelve  solid  angles. 

Location  of  Planes  by  Reference  to  Axes. — The  position  of 
any  plane  is  known  when  its  intercepts  on  the  assumed  axial 
directions  are  given.  If  #,  y,  z  represent  the  intercepts  on 
the  respective  axes  of  a  plane,  the  position  of  the  plane  may 
be  expressed  by  x  :  y  :  z.  The  intercepts  on  the  axes  are 


FIG.  6. 

called  the  parameters  of  the  plane.  In  general  the  axes  are 
lettered  a,  b,  c,  the  vertical  axis  usually  being  represented 
by  c,  that  from  right  to  left  b,  from  front  to  rear  by  a ;  as  in 
analytical  geometry,  the  positions  of  the  semiaxes  on  oppo- 
site sides  of  the  origin  have  opposite  signs,  the  plus  sign  (+) 
being  applied  to  the  halves  in  front,  to  the  right,  and  above 
the  origin,  and  the  minus  sign  (  — )  to  the  opposite  halves, 
Fig.  6.  If  definite  lengths  on  the  axial  directions  be 
assumed  as  unit  semiaxes,  the  parameters  of  any  plane  may 
be  expressed  in  these  lengths.  The  unit  semiaxes  assumed 
are  those  belonging  to  a  particular  crystal  form  of  each 


CR  YS TA LLOGRA PH Y. 

species.  This  particular  form  is  called  the  unit  form  or 
fundamental  form.  The  unit  form  and  the  crystallographic 
axes  in  the  form  are  so  chosen  as  to  give  the  simplest  ex- 
pression for  the  parameters  in  the  different  crystals  of  the 
species.  If  we  let  a,  b,  and  c  represent  the  unit  axes,  the 
parameters  x,  y,  and  z  of  any  plane  may  be  written  ma  :  nb  : 
re,  which  is  the  general  expression  for  a  face.  The  letters 
m,  ny  and  r  are  the  ratios  of  the  intercepts  to  the  lengths  of 
the  semiaxes  and  are  called  parameter  coefficients.  It  is 
evident  that  the  intercepts  of  all  parallel  planes  bear  the 
same  ratio  to  each  other,  and  since  crystallographic  sym- 
metry is  not  affected  by  shifting  a  plane  parallel  to  itself, 
one  of  the  intercepts  of  a  plane  may  always  be  assumed 
equal  to  unity,  and  the  general  expression  for  the  face 
becomes  a  :  nb  \  re.  It  follows  from  these  considerations 
that  all  parallel  planes  lying  on  the  same  side  of  the  origin 
have  identical  expressions ;  parallel  planes  on  the  opposite 
sides  of  the  origin  have  the  same  expressions  except  as  to 
sign.  Parallelism  to  any  axis  is  represented  by  the  sign  in- 
finity associated  with  that  axial  symbol.  Thus  a :  oo  b  :  oo  c 
indicates  a  plane  parallel  to  two  of  the  axes  (b  and  c}.  The 
positions  of  a  plane  may  also  be  expressed  by  using  the 
reciprocals  of  the  parameters ;  such  reciprocals  are  termed 
indices  of  the  plane.  Several  systems  of  notation  have  beea 
devised,  the  object  in  each  case  being  to  represent  briefly 
and  clearly  the  position  of  the  faces  with  reference  to  the 
crystallographic  axes.  It  is  not  practicable  to  here  describe 
the  system  of  notation. 

Definitions  Pertaining  to  Crystals. — Cleavage  is  the  quality 
which  minerals  possess  of  splitting  in  certain  definite 
directions  along  plane  surfaces.  Cleavage  is,  of  course,  a 
result  of  molecular  structure,  and  a  consideration  of  the 
molecular  arrangements  in  a  mineral  which  would  produce 
crystal  faces  explains  also  the  tendency  to  cleave  in  direc- 
tions parallel  to  the  faces.  Every  cleavage  plane  is  a  possi- 
ble face  of  a  crystal,  and  is  due  to  the  molecular  arrange- 
ment which  produces  faces.  The  more  fundamental  the 
face  the  more  perfect  is  the  cleavage  in  that  direction.  The 


^%€^e 


CRYSTALLOGRAPHIC  LAW.  $. 

natural  planes  of  a  crystal  are  called  its  faces ;  those  ob- 
tained by  splitting  are  called  cleavage  planes.  As  already 
stated,  the  intersections  of  bounding  planes  are  edges. 
When  an  edge  is  cut  off  by  a  plane  it  is  said  to  be  replaced / 
when  the  replacing  plane  is  equally  inclined  to  the  original 
faces  the  edge  is  truncated ;  when  the  edge  is  cut  off  by 
two  planes  equally  inclined  respectively  to  the  original  faces 
it  is  bevelled. 

Similar  planes  are  those  which  can  be  expressed  by  the 
same  notation  except  as  to  signs.  Similar  edges  are  pro- 
duced by  the  intersection  of  corresponding  pairs  of  similar 
planes.  Similar  angles  are  formed  by  the  meeting  of  the 
same  number  of  corresponding  similar  planes.  Planes  which 
have  like  positions  with  respect  to  the  axes,  except  as  to 
direction  from  the  center,  are  like  planes. 

Similar  planes  are  always  like  planes ;  thus  the  faces  of 
the  cube  are  all  like  planes,  but  only  the  opposite  faces  are 
similar  planes. 

Crystallographic  Law — Law  of  Axial  Ratios,  or  Rationality 
of  Parmeters  or  Indices. —From  what  has  preceded  we  see  that 
symmetry  is  inherent  in  nearly  all  solid  minerals  and  is  part 
of  their  nature.  Crystallographic  symmetry  may  be  con- 
sidered as  a  natural  result  of  the  molecular  structure  of  a 
mineral.  Certain  geometric  relations  have  been  found  to 
connect  all  the  faces  which  belong  to  the  crystals  of  any 
one  mineral. 

The  law  governing  these  relations  is  known  as  the  law  of 
axial  ratios,  or  the  law  of  rationality  of  parameters  or  indices. 
It  is  an  empirical  law,  but  there  are  no  known  exceptions  to 
it,  and  it  is  the  basis  of  mathematical  crystallography.  The 
law  may  be  stated  as  follows : 

The  ratios  of  the  intercepts  on  the  same  axis  by  the  different 
planes  of  a  crystal  can  only  be  o,  oo,  or  rational  numbers  ;  these 
ratios  can  never  be  irrational.  The  law  may  also  be  expressed 
thus  :  The  position  of  all  the  planes  of  a  crystal,  located  by  their 
intercepts,  can  always  be  expressed  by  numbers  bearing  a  simple 
ratio  to  the  relative  lengths  of  the  axes  of  the  unit  form. 

The  geometric  consequences  of  this  law  are  the  exclu- 


I O  CR  YS  TA  LLOGRA  PH  Y. 

sion  from  crystalline  forms  of  all  but  the  simpler  types  of 
symmetry  about  an  axis,  binary,  ternary,  quaternary,  and 
senary.  Regular  solids  of  a  higher  order  than  the  cube  or 
octahedron  are  thus  excluded. 

Constancy  of  Angles. — Since  the  planes  of  a  crystal  may 
be  shifted  without  affecting  crystallographic  symmetry — 
provided  each  plane  is  moved  parallel  to  itself — it  follows 
that  the  above  law,  the  constant  ratio  of  the  intercepts  for 
the  different  planes  of  the  crystal,  also  fixes  a  constant  angle 
between  the  intersecting  planes,  and  we  may  write  as  a 
second  crystallographic  law :  that  the  angles  of  inclination 
between  like  faces  of  the  crystals  of  the  same  species  are  constant. 

The  unequal  development  of  the  faces  of  a  crystal  during 
its  growth  has  the  same  effect  as  the  shifting  of  the  planes 
in  directions  parallel  to  themselves.  This  does  not  change 
the  ratios  existing  among  their  intercepts ;  hence  the  angles 
between  the  faces  is  constant,  however  much  the  faces  may 
vary  in  size  in  the  different  crystals  of  the  same  species. 

All  possible  classes  of  crystalline  forms  can  be  deduced 
mathematically,  in  the  same  manner  that  possible  geomet- 
rical polyhedrons  are  deduced,  and  the  solution  is  less  com- 
plex, for  the  law  of  axial  ratios  excludes  the  higher  orders 
of  symmetry.  The  possible  crystalline  classes  are  found, 
under  the  law,  to  be  thirty-two.  Natural  representatives  of 
all  the  possible  classes  are  not  yet  known,  though  nearly  all 
that  do  not  occur  in  nature  have  been  produced  in  the 
laboratory. 

Zonal  Relations. — The  planes  occurring  in  crystals  are  frequently  ar- 
ranged in  belts  extending  around  the  crystal  in  different  directions. 
A  zone  includes  a  series  of  faces  whose  intersections  are  all  parallel  to 
each  other.  An  imaginary  line  through  the  center  of  the  crystal,  par- 
allel to  the  common  direction  of  intersection,  is  called  the  zonal  axis. 
All  the  planes  which  belong  to  the  same  zone  are  said  to  be  tautozonal. 
The  zonal  relation  establishes  the  fact  that  the  parameters  of  the  faces 
of  the  same  zone  have  constant  ratios  for  two  of  the  axes. 

(i)  When  the  positions  of  two  planes  of  a  zone  are  known,  the 
direction  of  the  zonal  axis  is  determined.  The  position  of  a  plane  be- 
longing to  two  zones  is  known  when  the  directions  of  the  zonal  axes 
-are  known. 


CRYSTALLINE   SYSTEMS. 


II 


(2)  The  parameter  relations  between  the  faces  of  a  zone  make  it 
always  possible  to  deduce  some  simple  numerical  relation  between  the 
faces  belonging  to  the  same  zone  ;  the  relations  so  expressed  give  the 
zonal  equation.  The  determination  of  what  planes  belong  in  the  same 
zone  is  simple  in  principle,  and  not  especially  difficult  in  practice,  but 
the  method  to  be  pursued  cannot  be  here  explained. 

We  have  seen  that  the  symmetry  of  form  of  crystals  can  be  ex- 
pressed in  their  axial  relations,  according  to  the  number  and  character 
of  their  axes  of  symmetry.  On  this  basis  the  possible  groups  of  crystals 
are  generally  classed  in  six  systems,  depending  upon  the  number,  rela- 
tive lengths,  and  inclinations  of  their  crystallographic  axes. 


CRYSTALLINE   SYSTEMS. 


I.  The  Isometric  System. — This  system  has  three  equal 
axes  at  right  angles  to  each  other,  each  axis  being  an  axis  of 
quaternary  symmetry.  The  simplest  forms  under  this  system 
are  the  cube,  Fig.  7,  the  regular  octahedron,  Fig.  8,  and  the 


---, 


FIG.  7, 


FIG.  8. 


regular  dodecahedron,  Fig.  9.  The  positions  of  the  axes 
are  indicated  in  the  diagrams.  Either  of  these  forms  can  be 
assumed  as  fundamental  and  the  others  readily  derived  from 
it ;  for  example,  if  in  the  cube  planes  be  passed  parallel  to 
one  lateral  axis  and  through  the  extremities  of  the  vertical 
and  the  other  lateral  axis,  the  octahedron  will  result,  or  pass 
planes  through  the  extremities  of  the  semi-axes  of  the  octa- 
hedron, perpendicular  to  one  axis  and  parallel  to  the  other 
two,  and  the  intersections  will  form  the  edges  of  an  enclosing 
•cube.  The  faces  of  one  or  more  of  the  above  forms  are 


12 


CK  YS  TA  LLOGRA  PH  Y. 


sometimes  found  in  the  same  crystal,  as  shown  at  Figs.  10 
and  ii. 

Besides  the  crystallographic  axes  of  quaternary  symmetry  referred 
to  in  this  system,  there  are  other  axes  of  symmetry — six  axes  of  binary 


<^\    / 

I>\ 

r  "    N 

/  1 

J 

FIG.  9. 


FIG.  10. 


FIG.  ii. 


symmetry,  which  connect  the  middle  points  of  diagonally  opposite 
edges,  and  four  axes  of  ternary  or  trigonal  symmetry,  which  join  the 
vertices  of  opposite  solid  angles. 

II.  The   Tetragonal    System. — In    this    system   there   are 
three  axes,  at  right  angles  to  each  other;  the  two  lateral 
axes  are  equal  in  length,  and  the  vertical  axis  is  longer  or 
shorter.      The  simple  forms  in  this  system  are  the  right 
square  prisms,  Figs.  12,  and  13,  and  the  square  octahedrons, 
Figs.  14,  and  15.    The  cross-sections  of  these  forms,  perpen- 
dicular to  the  vertical  axes  are  squares.     As  mentioned  in 
the  preceding  system  these  forms  are  derivable  from  each 
other.     In  this  system  the  vertical  axis  is  an  axis  of  quater- 
nary or  tetragonal  symmetry.     The  lateral  axes  may  join  the 
centers  of  opposite  faces  or  of  opposite  vertical  edges.    The 
relative   lengths  of  the  vertical   and    horizontal   axes  may 
vary,  depending  upon  whether  a  long  or  short  octahedron 
be  assumed  as  the  unit  form.     The  selection  of  this  form 
depends  upon  considerations  already  mentioned. 

III.  The  Hexagonal  System. — This  system  has   two  divi- 
sions:  (a)  Hexagonal,   (b)  Rhombohedral.     (a)  In  the  hex- 
agonal division  there  are  four  axes,  one  vertical  and  three 
lateral  axes ;     the  lateral   making  angles  of    sixty  degrees 
with  each  other,  and  the  vertical  axis  being  perpendicular 


CRYSTALLINE   SYSTEMS. 


to  the  plane  of  the  lateral.  The  vertical  axis  is  an  axis  of 
senary  symmetry,  while  the  lateral  axes  are  of  binary  sym- 
metry. The  lateral  axes  are  in  sets  of  three  each,  the  axes 
of  each  set  being  equal  in  length,  (b)  In  the  rhombohedral 




•:^ 

- 

^ 

F 

IG. 

12 

FIG.  13. 


FIG.  14. 


FIG.  15. 


division  the  arrangement  of  certain  planes  around  the  verti- 
cal axis  are  alternate  in  the  upper  and  lower  halves  of  the 
crystal.  This  arrangement  leaves  the  vertical  axis  an  axis 
of  ternary  or  trigonal  symmetry  instead  of  hexagonal,  with 
three  horizontal  axes  of  binary  symmetry.  Some  of  the 
simpler  forms  of  the  hexagonal  division  are  shown  in  Figs. 


CRYSTALLOGRAPHY. 


16,  17,  and  18;  Fig.  19  shows  the  possible  positions  of  the 
lateral  axes  in  the  hexagonal  division;  Figs.  20  and  21  show 
two  forms  of  the  rhombohedral  division. 


/K 


\s             ' 

n 

FIG.  16. 


FIG.  17. 


FIG.  18. 


FIG.  19. 


FIG.  20. 


IV.  The  Orthorhombic  System.— This  system  has  three 
rectangular  axes,  no  two  of  which  are  of  the  same  length. 
The  simpler  forms  of  the  system  are  the  right  rectangular 
prism,  Fig.  22,  the  right  rhombic  prism,  Fig.  23,  and  the 
rhombic  octahedron,  Fig.  24.  The  planes  of  these  three 
forms,  as  well  as  of  others  not  mentioned,  are  sometimes 
found  in  the  same  crystal. 

In  this  system  each  axis  is  an  axis  of  binary  symmetry. 


CRYSTALLINE   SYSTEMS. 


V.  The  Monoclinic  System.— This  system  has  a  vertical 
and  two  lateral  axes,  no  two  being  of  the  same  length.  One 
lateral  axis  is  oblique  to  the  vertical  axis,  and  the  other 


^^                I 

^^ 

I 

L 

^\ 

u  \= 

FIG.  21. 


FIG.  22. 


i 

j 

I 

i 
i 

^_J 

i 

-i  — 

FIG.  23. 


FIG.  24. 


lateral  axis  is  perpendicular  to  the  plane  of  the  vertical  and 
oblique  lateral  axis.  The  simple  forms  in  the  system  are 
the  rhombic  prism,  Fig.  25,  the  oblique  rectangular  prism, 
Fig.  26,  and  the  right  rhomboidal  prism.  As  in  the  other 
systems,  the  planes  of  different  forms  sometimes  occur  hi 
the  same  crystal. 


CR  YS  TA  LLOGRA  PH  Y. 


In  different  species  belonging  to  this  system  the  relative 
lengths  and  inclinations  of  the  axes  vary. 

The  system  has  only  one  axis  of  binary  symmetry. 

VI.  The  Triclinic  System. — This  system  has  three  axes  of 
unequal  length,  each  being  oblique  to  the  plane  of  the  other 


-i — .f- 

/! 

:- i — 

/ 


7 


FIG.  25. 


two.  A  simple  form  is  the  oblique  rhomboidal  prism.  In 
different  species  belonging  to  this  system,  as  in  the  preced- 
ing, both  the  relative  lengths  and  inclinations  of  the  axes 
vary. 

There  is  no  axis  of  symmetry  in  this  system,  the  symmetry  existing 
only  with  respect  to  a  point  which  is  a  center  of  symmetry.  In  this 
case,  if  an  imaginary  plane  be  passed  through  the  center  parallel  to  one 
of  the  faces  and  the  portion  of  the  crystal  on  one  side  of  the  plane  be 
thought  of  as  rotated  180°  about  a  line  perpendicular  to  the  plane  and 
passing  through  the  center,  the  two  halves  of  the  crystal  would  then  be 
mirror  images  of  each  other  across  the  plane.  The  center  of  symmetry 
of  the  polyhedron  is  also  a  center  of  symmetry  for  every  polygonal 
figure  formed  by  the  intersection  of  the  faces  of  the  crystal  with  a  plane 
passing  through  the  center.  Every  such  polygon  rotated  in  the  plane 
about  the  center  occupies  congruent  positions  after  every  turn  of  180 
degrees. 

It  will  be  observed  that  the  above  systems  can  be  grouped  into  three 
classes,  depending  upon  the  number  of  their  principal  axes  of  sym- 
metry. A  principal  axis  of  symmetry  has  already  been  defined  as  one 
that  is  of  the  third  or  higher  order  of  symmetry.  This,  as  a  general 
statement,  is  correct,  and  any  crystal  which  has  trigonal  symmetry  has 
a  principal  axis  of  symmetry,  but  an  axis  of  trigonal  symmetry  is  not 
necessarily  a  principal  axis  of  symmetry  in  a  system  where  there  are 
axes  of  higher  symmetry.  Thus,  in  the  cube  (isometric),  the  three  axes 
of  tetragonal  symmetry  connecting  the  middle  point  of  opposite  faces 


CRYSTALLINE  SYSTEMS.  1 7 

are  principal  axes,  while  the  four  axes  of  trigonal  symmetry  connecting 
diagonal  opposite  angles  are  secondary  axes  in  this  system. 

The  groups  of  the  above  six  systems  according  to  the  number  of 
their  principal  axes  are : 

i st.  Those  without  a  principal  axis  of  symmetry.  Under  this  group 
are  included  the  Triclinic,  the  Monoclinic,  and  the  Orthorhombic.  The 
first  is  without  linear  symmetry,  and  the  other  two  have  only  binary 
symmetry. 

2d.  Those  with  one  principal  axis  of  symmetry.  Under  this  group 
are  the  Hexagonal  and  Tetragonal ;  the  principal  axis  in  the  first  being 
one  of  senary  symmetry,  and  in  the  second  of  quaternary. 

3d.  Those  with  three  principal  axes  of  symmetry.  The  Isometric  is 
the  only  system  in  this  group;  the  three  principal  axes  of  the  system 
being  of  quaternary  symmetry. 

Crystal  Symmetry  about  Planes.— In  grouping  the  crystal  forms  ac- 
cording to  their  axial  relations,  only  symmetry  about  lines  and  points 
has  been  described,  but  it  is  evident  that  symmetry  about  lines  involves 
symmetry  with  reference  to  planes.  The  crystallographic  axes  assumed 
in  the  first  four  systems  of  crystallization  result  from  the  intersection  of 
planes  of  symmetry.  In  the  Monoclinic  system  there  is  one  axis  of 
binary  symmetry,  which  must  accordingly  be  perpendicular  to  a  plane 
of  binary  symmetry.  In  the  Triclinic  system,  there  being  no  axis  of 
symmetry,  there  is  no  plane  of  symmetry.  Axes  of  symmetry  are  said 
to  be  like  or  equivalent  when  they  are  of  the  same  order  of  symmetry 
and  of  the  same  length.  Planes  of  symmetry  are  like  when  they  divide 
the  perfect  form  into  identical  halves.  In  general  a  plane  which  con- 
tains two  or  more  like  axes  of  symmetry  is  a  principal  plane  of  sym- 
metry, the  others  are  secondary  planes;  this  statement  must  be  limited 
in  the  isometric  system,  so  that  the  like  axes  shall  be  those  of  the 
highest  symmetry.  Principal  axes  of  symmetry  are  normal  to  principal 
planes  of  symmetry,  and  secondary  axes  to  secondary  planes.  From 
the  above  definition  it  is  seen  that  in  the  isometric  system  the  assumed 
coordinate  or  crystallographic  axes  are  the  principal  axes  formed  by  the 
intersections  of  the  principal  planes  of  symmetry.  In  the  tetragonal 
system  these  coordinate  axes  are  formed  by  the  intersection  of  one 
principal  plane  of  symmetry,  with  two  secondary  planes  of  symmetry, 
all  at  right  angles  to  each  other. 

In  the  Hexagonal  the  assumed  axes  are  formed  by  the  intersection  of 
one  principal  plane  with  six  secondary  planes  meeting  at  angles  of  30°. 

In  the  Orthorhombic  system  the  coordinate  axes  are  formed  by  the 
intersection  of  three  secondary  planes,  all  at  right  angles  to  each  other. 
In  the  Monoclinic  system  one  of  the  crystallographic  axes  is  the 
normal  to  the  plane  of  symmetry;  the  other  two  are  in  that  plane  and 
so  chosen  as  to  give  greatest  convenience  :  the  positions  of  these  latter 
are  usually  taken  as  previously  stated. 


18 


CR  YS  TA  LLOGRA  PH  Y. 


In  the  Triclinic  system  there  are  neither  planes  nor  axes  of  sym- 
metry, and  the  choice  of  coordinate  axes  is  arbitrary. 

Hexagonal  symmetry,  of  necessity,  includes  trigonal  symmetry,  and 
tetragonal  symmetry  includes  binary  symmetry. 

Crystal  Forms — Closed  and  Open  Forms. — A  form  in  crystallography  in- 
cludes all  of  the  like  faces  in  the  crystal — like  faces,  as  already  denned, 
being  those  which  have  like  positions  with  reference  to  the  axes,  except 


FIG.  27. 


FIG.  28. 


FIG.  29. 


FIG.  30. 


as  to  their  direction  from  the  origin.  If  all  the  faces  of  the  crystal  are 
like,  they  constitute  a  closed  form  ;  that  is,  the  enclosed  solid  is  entirely 
bounded  by  like  faces.  If  the  like  faces  do  not  enclose  the  solid,  the. 


DISTORTIONS  IN  CRYSTALS.  ig 

form  is  open.  There  are  no  closed  forms  in  the  Monoclinic  and  Tri- 
clinic  systems — that  is,  no  crystal  forms  in  which  all  the  faces  are  like  ; 
in  the  other  four  systems  there  are  closed  forms,  those  in  which  the 
crystal  faces  are  all  alike.  The  maximum  number  of  like  faces  in  the 
closed  forms  of  these  systems  varies  with  the  symmetry  of  the  system. 
The  number  is  48  in  the  Isometric,  24  in  the  Hexagonal,  16  in  the 
Tetragonal,  and  8  in  the  Orthorhombic,  which  are  shown  at  Figs.  27, 
28,  29,  and  30.  The  opposite  pairs  of  the  faces  in  these  forms  are  simi- 
lar planes. 

Holohedral  and  Hemihedral  Forms. — When  a  crystal  is  contained  by  all 
the  faces  necessary  to  the  complete  symmetry  of  the  system,  to  each 
face  there  is  a  parallel  similar  face,  the  total  number  being  even  and 
never  less  than  six ;  such  forms  are  holohedral.  There  are  occurring 
forms  in  which  there  are  only  one-half  or  one-fourth  the  number  of 
faces  necessary  to  complete  symmetry;  these  are  called  respectively 
hemihedral  and  tetrahedral  forms. 

These  forms,  other  than  the  holohedral,  may  be  considered  as  pro- 
duced by  the  suppression  of  one-half  or  three-fourths  of  the  planes  of 
the  complete  forms,  and  the  extension  of  the  remaining  planes  until 
they  intersect.  The  surviving  and  suppressed  planes  in  these  forms  are 
always  those  which  fulfill  certain  definite  conditions.  One-half  or 
three-quarters  of  the  planes  of  a  complete  form,  arbitrarily  chosen  for 
suppression  or  extension,  will  not  produce  the  other  forms.  The  sym- 
metry of  the  hemihedral  and  tetrahedral  forms  is  of  a  lower  order  than 
that  of  the  complete  forms  in  the  same  system.  The  symmetrical  ele- 
ments of  the  lower  forms  are  less  in  number,  but  identical  with  the  sym- 
metrical elements  in  the  holohedral  forms,  and  well-defined  geometrical 
laws  connect  the  forms  with  each  other. 

DISTORTIONS    IN   CRYSTALS. 

It  has  been  already  stated  that  crystallographic  symmetry  is  not 
always  accompanied  by  geometric  symmetry.  For  the  purpose  of  de- 
scribing the  systems,  it  is  simpler  to  consider  the  ideal  forms  as  we 
have  done,  but  the  perfect  forms  of  the  systems  seldom  occur  in  nature. 
The  departures  from  the  ideal  forms  which  are  due  to  the  unequal 
development  of  the  faces  of  the  crystal  and  to  the  unequal  dimensions 
of  like  axes  are  called  distortions. 

Distortions  render  more  difficult  the  identification  of  forms,  but  the 
constancy  of  interfacial  angles  and  the  identical  characters  of  like  faces 
are  the  means  by  which  the  difficulty  is  overcome.  For  example,  the 
perfect  cube  is  not  generally  met  with  in  nature;  if  lengthened  or 
shortened  in  the  direction  of  one  axis,  it  assumes  the  form  of  a  right 
square  prism ;  if  varied  in  the  direction  of  two  axes,  it  becomes  a  rect- 
angular prism  (see  Figs.  4  and  5).  In  the  first  case  its  geometric  form 


20 


CR  YSTALLOGRAPHY. 


would  place  it  in  the  tetragonal  system,  in  the  second  case  in  the 
orthorhombic.  The  physical  similarity  of  its  faces,  or  equal  cleavage  in 
the  three  rectangular  directions,  would  place  it  in  its  proper  system. 

Other  forms  more  complex  than  the  cube  have  distortions  not  so 
readily  recognized,  but  the  considerations  above  mentioned,  together 
with  a  general  familiarity  with  the  more  common  distortions,  usually 
serve  to  place  the  specimen  under  consideration.  The  faces  of  crystals 
are  frequently  not  plane  surfaces:  they  may  be  either  striated  or  curved, 
These  imperfections  in  crystals  may  result  from  oscillatory  combinations 
or  twinning,  to  which  reference  will  be  made.  Curvature  is  also  some- 
times due  to  mechanical  causes,  as  is  thought  to  be  the  case  in  tourma- 
line, or  to  the  molecular  conditions  of  crystallization,  as  in  the  diamond. 


MULTIPLE  CRYSTALS. 

The  crystal  individuals  thus  far  considered  have  all  been  polyhe- 
drons, whose  interfacial  angles  are  less  than  180°.  Such  is  always  the 
case  with  the  distinct  individual.  On  many  crystalline  surfaces  re- 
entering  angles  are  found  which  always  indicate  a  combination  of  two 
or  more  individuals.  These  groups  of  crystals  conform  to  certain  defi- 
nite laws.  A  few  of  the  important  groups  will  be  briefly  referred  to. 

Parallel  Grouping. — The  simplest  cases  of  parallel  grouping  consist 
of  similar  crystals  so  arranged  that  the  line  joining  their  centers  coin- 
cides with  a  crystallographic  axis  or  is  parallel  to  it.  These  forms  are 
illustrated  in  Figs.  31,  32,  33.  If  two  cubes  were  joined  as  are  the  forms 
in  Fig.  31,  there  would  result  a  right  square  prism  which  would  appear 


FIG.  31. 


FIG.  32. 


FIG.  33- 


as  a  single  crystal.     The  re-entering  angles  denote  the  junction  of  sepa- 
rate individuals  in  parallel  growth. 

If  the  width  of  the  alternating  planes  is  very  small,  there  results  what 


* 


MULTIPLE   CRYSTALS.  21 

appears  to  be  a  single  crystal  with  striated  faces ;  this  arrangement  of 
planes  in  a  surface  is  termed  oscillatory  combination  ;  there  is  an  ap- 
proximation to  this  in  Fig.  33. 

Often  complex  crystalline  forms  result  from  parallel  growths.  Many 
of  the  delicate  dendritic  forms  are  thus  brought  about.  In  these  par- 
allel groupings  the  crystal  as  a  whole  is  symmetrical  with  reference  to 
some  plane  which  is  also  a  plane  of  symmetry  for  each  individual  form. 

Twin  Crystals. — In  twinning  combinations  two  individual  crystals  or 
two  halves  of  the  same  crystal  are  joined  so  as  to  have  either  a  common 
crystallographic  direction  or  crystallographic  plane,  but  the  parts  are 
not  in  completely  parallel  positions.  The  two  crystals  or  two  halves  of 
the  same  crystal  are  accordingly  symmetrical  with  reference  to  a  plane 
which  is  not  a  plane  of  symmetry  for  the  individuals,  and  this  is  the 
main  distinction  between  the  parallel  grouping  and  the  twinning  posi- 
tion. 

The  relation  of  the  parts  in  a  twin  crystal  may  be  understood  from 
Fig.  34,  which  shows  a  regular  octahedron  divided  into  halves  by  a  plane 
parallel  to  an  octahedral  face ;  in  the  figure  the  front  half  has  been 
rotated  through  180°  about  an  axis  normal  to  the  plane. 

Contact  Twins. — The  form  of  structure  shown  in  Fig.  34  is  an  exam- 
ple of  what  is  designated  as  contact  twins  ;  this  particular  form  is  also 
termed  a  hemitrope  crystal.  Another  form  of  contact-twinning  is- 
shown  at  Fig.  35. 

Penetration  Twins  are  those  in  which  the  twinning  crystals  are  not 
joined  along  a  plane,  but  more  or  less  completely  penetrate  each  other. 
Such  forms  are  shown  at  Figs.  36,  37,  and  38. 

Repeated  Twinning. — A  third  individual  may  be  added  to  one  of  the 
two  crystals  of  a  twin  according  to  the  same  law  that  joins  the  first  two, 
thus  causing  repeated  twinnings,  giving  rise  to  trillings,  fourlings,  five- 
lings,  etc.  The  variations  of  form  resulting  from  the  different  applica- 
tions of  the  twinning  laws  are  very  numerous,  and  further  reference  to 
them  cannot  be  here  undertaken. 

Pseudomorphs. — Minerals  generally  belonging  to  one  crystalline  sys- 
tem are  sometimes  found  to  have  the  form  of  another.  Such  crystals 
are  called  pseudomorphs.  They  are  thought  to  result  sometimes 
through  a  change  of  composition  in  the  mineral,  or  else  the  pseu- 
domorph  is  formed  by  the  filling  of  a  cavity  left  by  the  removal  of  a 
crystal  of  another  form. 

ISOMORPHISM. 

Some  of  the  compounds  of  certain  elements  crystallize 
in  the  same  form  ;  and  not  only  this,  but  one  of  these  ele- 
ments may  replace  the  others  in  a  crystal  without  destroying 


22 


CR  YS  TA  LLOGRA  PH  Y. 


FIG.  34. 


FIG.  35. 


FIG.  36. 


FIG.  37- 


FIG.  38. 


CRYSTALLINE  AGGREGATES.  2$ 

the  form  ;  such  elements  are  said  to  be  isomorphous.     Cal- 
cium, magnesium,  and  iron  are  notable  examples. 


CRYSTALLINE  AGGREGATES. 

Most  mineral  masses  are  not  composed  of  distinct  crystal 
forms,  but  consist  of  an  aggregation  of  imperfect  crystals. 
Sometimes  the  aggregation  is  wholly  irregular,  and  some- 
times more  or  less  regular.  There  are  many  varieties  of 
aggregates.  The  planes  between  the  individuals  in  aggre- 
gates are  simply  planes  of  fracture  ;  when  the  fracture  gives 
rise  to  a  coarse  rough  surface  it  is  called  hackly ;  when  it 
gives  rise  to  a  smooth  flat  surface  it  is  called  even;  and  when 
it  gives  rise  to  curved  surfaces,  having  shell-like  appear- 
ances, it  is  called  conchoidal.  Some  of  the  more  important 
and  common  aggregates  are  : 

1.  Dendritic. — Composed  of    small  crystals  arranged   in 
such  a  manner  as  to  give  a  tree-like  appearance,  as  in  native 
gold  and  silver.     The  term  is  also  frequently  used  for  simi- 
lar forms,  whether  due  to  crystals  or  not,  as  to  those  pro- 
duced by  the  oxide  of  manganese 

2.  Drusy. — Composed  of  many  small  crystals  implanted  in 
a  finer  ground-mass,  giving  a  very  rough  surface. 

3.  Columnar    or    Fibrous. — Composed    of    columnar    or 
fibrous  individuals,  sometimes  aggregated  so  as  to  give  the 
appearance  of  a  heterogeneous  mixture,  sometimes  forming 
star-like  groups,  and   sometimes   giving   rise    to   globular 
forms.     These  globules  are  sometimes  arranged   so   as  to 
give  rise  to  forms  resembling  bunches  of  grapes,  and  there- 
fore   called    botryoidal.     If   the   globular  masses  be  nearly 
hemispheres,  the  form  is  called  mammillary. 

4.  Lamellar. — Consists  of  plates  or  leaves.     If  the  plates 
are  very  thin  and  easily  separable,  the  structure  is  foliated, 
especially  if  the  plates  are  minute  scales.     The  varieties  of 
mica  well  illustrate  this  structure. 

5.  Granular. — Composed  of  grains,  either  coarse  or  fine  ; 
sometimes   so   fine  that  they  cannot  be   detected    by  the 
microscope,  then  said  to  be  cryptocrystalline ;  sometimes  of 


24  CRYSTALLOGRAPHY. 

the  size  of  peas,  giving  rise  to  pisolitic  forms  ;  sometimes  of 
the  size  of  the  roe  of  fish,  giving  rise  to  oolitic  forms ;  some- 
times flattened  like  lenses,  giving  rise  to  lenticular  forms. 

6.  Concretions. — Vary  in    shape    from    simple    spherical 
masses  to  very  grotesque  aggregations,  but  always  rounded 
in  form.    The  more  perfect  forms  often  consist  of  concentric 
layers.     The  individual  grains  present  in  the  granular  for- 
mations are  often  concretions,  as  in  the  oolitic.    One  form  of 
concretion,  intersected  by  cracks  which  have  been  filled  by 
foreign  matter,  is  called  a  septarium  or  turtle-stone. 

7.  Stalactitic. — Cylindrical  or  conical  in  shape,  composed 
of  fine  grains,  fibers,  or  lamellae  deposited  from  solution. 

7.  Stratified. — Composed  of  layers,  sometimes  of  the  same 
color    throughout,  sometimes   of    different   colors,  giving 
rise  to  banded  forms;  the  layers  are  formed  by  successive 
deposition. 

8.  Geodes. — Forms  resulting  from  incomplete  filling  of  a 
cavity  by  a  mineral,  the  interior  often  being  covered  witk 
crystals. 


*/t«£ 


CHAPTER   II. 

PHYSICAL  AND   CHEMICAL   PROPERTIES    OF   MINERALS, 
PHYSICAL   PROPERTIES   OF   MINERALS. 

THE  properties  of  minerals  which  are  useful  in  deter- 
minative mineralogy  are  of  two  kinds,  viz.,  physical  and 
chemical.  The  more  important  physical  properties  and 
those  which  can  be  most  readily  observed  are  (i)  luster,  (2) 
color,  (3)  hardness,  (4)  streak,  (5)  malleability,  (6)  taste,  odor, 
and  feel,  (7)  specific  gravity. 

Luster. — There  are  two  general  classes  of  luster,  (i) 
metallic,  (2)  unmetallic.  Metallic  luster  includes  semi-metal- 
lic ;  the  name  of  the  luster  indicates  the  nature  in  each  case. 
Unmetallic  luster  includes  (i)  vitreous,  (2)  resinous,  (3) 
pearly,  (4)  greasy ;  again,  the  name  indicates  the  character 
in  each  case. 

Color. — The  mineral  kingdom  displays  a  great  variety  of 
colors.  Colors  are  generally  important  only  in  the  case  of 
pure  specimens.  Some  of  the  more  common  mineral  colors 
are  red,  yellow,  white,  gray,  brown,  and  black.  A  mineral 
is  said  to  be  opalescent  when  a  milky,  pearly,  or  glistening 
reflection  is  obtained  from  it ;  phosphorescent  when  it  emits 
light  by  friction  or  by  being  heated  ;  iridescent  when  it  gives 
rainbow  colors  from  the  interior.  When  a  mineral  reflects 
prismatic  colors  upon  being  turned  in  the  light  it  is  said  to 
give  a  play  of  colors. 

Streak. — This  is  the  name  given  to  the  color  of  the  pow- 
der obtained  by  abrading  the  mineral,  or  to  the  color  of  the 
streak  obtained  by  drawing  it  across  a  small  plate  of 
white  porcelain. 

25 


26  PHYSICAL  AXD   CHEMICAL  PROPERTIES  OF  MINERALS. 

Hardness. — The  hardness  of  minerals  is  determined  by  the 
use  of  a  file.  Care  must  be  exercised  in  selecting  a  portion 
of  the  specimen  to  be  rubbed  with  the  file,  as  the  true  hard- 
ness will  not  be  obtained  upon  very  acute  angles,  or  upon 
parts  altered  by  exposure.  The  sound  emitted  as  the  file  is 
drawn  across  the  specimen  is  often  as  good  a  guide  as  the 
ease  with  which  the  specimen  is  abraded.  For  purpose  of 
comparison,  the  following  scale  of  hardness  is  adopted: 
i,  talc ;  2,  rock  salt ;  3,  calcite  ;  4,  fluorite ;  5,  apatite  ;  6,  ortho- 
clase ;  7,  quartz ;  8,  topaz  ;  9,  sapphire ;  10,  diamond. 

Malleability. — When  portions  of  a  mineral  can  be  flat- 
tened under  the  hammer  it  is  said  to  malleable. 

Brittleness. — When  a  mineral  crumbles  under  the  applica- 
tion of  a  force  it  is  said  to  be  brittle. 

Flexibility. — When  a  mineral,  or  part  of  it,  will  bend  and 
remain  bent  upon  the  relief  of  the  force  it  is  said  to  be 
flexible ;  when  it  will  return  to  the  original  position  upon 
the  relief  of  the  force  it  is  said  to  be  elastic. 

Sectility. — Refers  to  the  property  possessed  by  some 
minerals  of  being  cut  into  thin  slices  without  crumbling,  but 
which  crumble  under  the  hammer. 

Odor. — Odors  are  developed  by  moisture,  heat,  or  acids ; 
only  a  few  common  ones  need  description : 

Argillaceous  Odor. — That  of  moist  clay,  developed  when  a 
clayey  mineral  is  breathed  upon. 

Alliaceous  Odor. — That  of  garlic,  developed  when  the 
arsenical  minerals  are  heated  by  friction  or  by  the  blow- 
pipe. 

Sulphurous  Odor. — That  of  burning  sulphur,  developed  by 
heating  some  of  the  sulphides  in  air,  or  by  burning  sulphur. 

Feel. — Some  minerals  have  characteristic  greasy,  rough, 
or  smooth  feel. 

Specific  Gravity. — The  specific  gravity  of  a  substance  is 
the  ratio  of  the  weight  of  a  given  volume  of  the  substance 
to  the  weight  of  an  equal  volume  of  water  at  a  standard 
temperature.  One  of  the  simplest  ways  to  determine 
specific  gravity  is  to  obtain  the  weight  of  a  small  piece  of 
the  mineral,  and  then  to  obtain  the  weight  of  this  same 


CHEMICAL   PROPERTIES   OF  MINERALS.  2/ 

piece  immersed  in  water.  These  observations  are  sufficient 
to  determine  the  specific  gravity  for  ordinary  purposes. 
There  are  specially  contrived  balances  for  taking  these 
weights. 

For  porous  minerals  the  specific  gravity  is  obtained  by 
the  use  of  a  bottle  of  standard  capacity  by  weight.  A 
known  weight  of  water  is  poured  from  the  bottle  and  then 
the  powdered  mineral  is  added  until  the  volume  of  the 
water  is  the  same  as  before.  From  the  original  weight  of 
water,  from  the  weight  of  the  water  removed,  and  from  the 
weight  of  the  water  with  the  mineral  added  the  specific 
gravity  can  be  obtained. 

This  method  is  of  course  equally  applicable  to  compact 
minerals. 

For  minerals  soluble  in  water  a  liquid  must  be  used 
which  will  not  dissolve  them  and  whose  specific  gravity  is 
known. 

The  physical  properties  are  of  great  importance  in  deter- 
minative mineralogy  and  many  common  species  can  be 
approximately  determined  by  them. 

Tables  to  assist  in  the  determination  of  the  minerals 
described  are  included  in  the  text.  These  tables  have  been 
prepared  by  classifying  the  minerals  according  to  luster, 
subclassifying  under  luster  according  to  color,  color  of 
streak,  or  hardness.  Other  physical  properties  are  tabu- 
lated, and  a  column  of  remarks  noting  characteristics,  not 
elsewhere  included,  is  added. 

/'.  •/ 

CHEMICAL    PROPERTIES    OF    MINERALS. 

£/   ,/  tnr 

If  a  specimen  cannot  be  fully  determined  by  the  physical 
tests,  the  chemical  properties  must  be  considered.  While 
the  chemical  tests  will  often  afford  a  ready  means  for 
determining  a  specimen,  it  is  always  better  to  consider 
physical  characters  first. 

For  examining  the  chemical  properties  of  minerals  the 
following  facilities  are  usually  to  be  had  in  the  laboratory : 
hammer,  anvil,  steel  mortar,  agate  mortar,  forceps,  open  and 


28   PHYSICAL  AND   CHEMICAL  PROPERTIES  OF  MINERALS* 

and  closed  tubes,  charcoal,  blowpipe,  platinum  wire,  fluxes, 
and  reagents. 

Hammer  and  Anvil. — These  are  for  removing  small  pieces 
from  the  specimen  for  subsequent  treatment.  By  holding 
the  specimen  on  the  anvil  a  sharp  blow  properly  adminis- 
tered will  usually  separate  a  suitable  fragment. 

Steel  Mortar. — This  is  used  for  powdering  the  fragment, 
and  the  mortar  should  always  be  placed  on  the  anvil  for 
use.  The  agate  mortar  and  pestle  are  used  for  further  pul- 
verization by  friction  of  the  power  obtained  from  the  steel 
mortar. 

Forceps. — Any  forceps  provided  with  platinum  tips  will 
answer ;  but  those  so  made  that  the  tips  will  press  together 
of  themselves  will  be  found  most  convenient.  The  forceps 
are  used  in  connection  with  the  blowpipe  for  fusing,  or  for 
detecting  a  volatile  ingredient,  which  may  yield  an  odor  or 
color  the  flame.  Only  a  small  thin  sliver  of  the  specimen 
should  be  used,  and  it  should  be  held  so  as  to  project  well 
beyond  the  point  of  the  forceps.  Minerals  easily  reduced  to 
the  elementary  state  should  not  be  heated  in  contact  with 
the  forceps,  and  as  a  rule  it  is  well  not  to  use  the  forceps 
with  those  having  metallic  luster. 

Charcoal. — Charcoal  is  used  as  a  support  upon  which 
various  bodies  are  heated.  The  heating  may  be  for  the 
purpose  of  fusing,  for  volatilizing,  or  for  the  production  of 
a  sublimate.  The  odor  from  the  volatilized  body  and  the 
color  of  the  sublimate,  near  and  at  a  distance  from  the 
assay,  are  often  characteristic.  An  infusible  and  non-volatile 
residue  can  often  be  subjected  to  additional  treatment. 

Besides  serving  as  a  support  as  above  indicated,  the 
reducing  power  of  the  charcoal  is  often  made  use  of  to 
deoxidize  certain  bodies,  as  metallic  oxides.  The  production 
of  sublimates  is  often  facilitated  by  the  use  of  fluxes.  Easily 
reducible  compounds,  as  those  of  lead,  zinc,  arsenic,  and 
antimony,  should  always  be  heated  on  charcoal  and  not  in 
the  forceps. 

Open  Tubes. — These  are  used  to  heat  the  mineral  in  con- 
tact with  air.  A  small  fragment,  or  better  some  of  the 


CHEMICAL   PROPERTIES   OF  MINERALS.  2$ 

powdered  mineral,  is  put  in  the  tube  and  the  tube  heated, 
being  held  as  highly  inclined  as  possible;  the  result  to  be 
expected  will  of  course  depend  upon  the  particular  mineral, 
and  the  observations  to  be  noted  are  indicated  in  the  tabular 
description  of  the  species. 

Closed  Tubes. — These  are  used  for  heating  the  mineral 
out  of  contact  with  air  and  for  making  tests  with  liquid 
reagents.  Only  a  very  small  quantity  of  the  mineral  must 
be  used  except  in  cases  particularly  specified,  and  only  a 
small  quantity  of  acid  is  necessary.  Attention  is  called  to 
the  phenomena  to  be  observed,  in  the  tables  above  re- 
ferred to. 

Blowpipe. — The  blowpipe  is  simply  a  bent  tube,  with  a 
very  narrow  orifice,  provided  with  a  platinum  tip  which  can 
be  removed  and  cleaned.  Only  very  small  pieces  or  amounts 
of  mineral  must  be  used  before  the  blowpipe. 

In  using  the  blowpipe  it  is  necessary  to  blow  and  breathe 
at  the  same  time,  for  results  can  generally  be  accomplished 
only  by  continued  application  of  the  flame  for  some  time. 
This  accomplishment  is  readily  acquired  by  practice.  Care 
must  be  taken  that  the  flame  be  well  protected  from  draft 
or  anything  which  would  cause  flickering.  The  flame 
should  be  colorless,  for  the  characteristic  colors  of  many 
minerals  are  readily  developed  before  the  blowpipe. 

Platinum  Wire. — This  is  used  for  facilitating  the  action 
of  the  fluxes  on  the  minerals  and  for  affording  opportunity 
for  observing  the  action ;  such  action  frequently  gives 
characteristic  colors.  In  general  the  manner  of  using  the 
wire  is  as  follows  :  Twist  it  into  a  small  loop  at  the  end,  heat 
it,  and  dip  it  into  the  flux,  and  fuse  to  a  clear  bead,  then 
into  the  powdered  mineral,  and  fuse  again  ;  repeat  the  opera- 
tion and  observe  carefully  the  fused  mass,  which  is  called 
a  bead.  The  blowpipe  may  or  may  not  be  used  in  heating 
the  beads;  in  some  cases  the  beads  have  one  color  in 
the  oxidizing  flame  and  another  in  the  reducing  flame,  as 
described  in  the  tables. 

Fluxes. — The  common  fluxes  for  making  beads  are  borax, 
sodium  borate,  salt  of  phosphorus,  phosphate  of  sodium  and 


30  PHYSICAL  AND  CHEMICAL  PROPERTIES  OF  MINERALS. 

ammonium,  and  soda,  sodium  carbonate.  They  owe  their 
value  to  the  fact  that  they  dissolve  or  combine  with  metallic 
oxides,  giving  characteristic  colors ;  the  mineral  should  be 
roasted  before  making  a  bead,  so  that  the  oxide  will  be 
formed  if  it  is  not  already  present. 

Soda  is  a  very  valuable  flux  for  decomposing  the 
metallic  compounds. 

Reagents. — The  more  common  and  useful  reagents  are 
sulphuric,  hydrochloric,  and  nitric  acids,  ammonia,  am- 
monium sulphide,  potassium  ferrocyanide,  and  ammonium, 
oxalate. 


SOME    IMPORTANT    AND    COMMON    MINERAL    TESTS. 

(These  should  be  learned  at  once  by  the  student.) 

Before  the  Blowpipe — Copper. — Copperminerals  moistened 
with  hydrochloric  acid  give  the  flame  an  azure-blue  color ; 
heated  alone  the  flame  is  colored  green. 

Iron. — Minerals  containing  iron  are  converted  into  mag- 
netic oxide  in  the  reducing  flame;  sometimes  soda  is  re- 
quired. 

Lead. — Lead  minerals  heated  on  charcoal  with  soda  give 
a  yellow  oxide  coating  on  charcoal  and  leave  a  lead  globule. 

Zinc. — Important  zinc  ores  when  heated  on  charcoal 
give  a  coating  of  oxide,  yellow  while  hot,  but  white  on 

cooling. 

Open-tube  Tests. — Arsenic. — The  common  arsenical  com- 
pounds give  a  white  sublimate  of  arsenious  oxide  on  the 
tube,  an  alliaceous  odor,  and  an  acid  reaction  with  litmus 
paper. 

Sulphur. — Sulphides  give  an  odor  of  sulphurous  oxide 
and  an  acid  reaction. 

Closed-tube  Tests. — Arsenic. — The  common  arsenic  com- 
pounds in  a  closed  tube  give  a  coating  of  arsenic,  a  coating 
of  red  and  yellow  orpiments  if  sulphur  be  present,  and  emit 
an  alliaceous  odor. 

Carbon. — Carbon  mixed  with  a  nitrate  and  heated  will 
deflagrate. 


MISCELLANEOUS    TESTS.  3 1 

Copper. — To  test  for  copper  treat  with  nitric  acid  and  add 
excess  of  ammonia ;  if  copper  be  present,  a  blue  solution  is 
given  ;  copper  sulphides  must  first  be  well  roasted. 

Calcium. — To  test  for  calcium  treat  with  hydrochloric 
acid,  neutralize  with  ammonia,  add  a  soluble  oxalate,  and 
calcium  oxalate  will  fall. 

Iron. — To  test  for  iron  treat  with  hydrochloric  acid,  add 
potassium-ferrocyanide,  and  a  blue  precipitate  will  be 
formed. 

Mercury. — To  test  for  mercury  mix  a  salt-spoonful  with 
twice  its  volume  of  soda,  heat,  and  globules  of  mercury  will 
be  deposited  on  the  cool  sides  of  the  tube. 

Water. — To  test  for  water  put  the  powdered  mineral  in 
the  tube,  heat  the  latter  held  in  a  nearly  horizonal  position  ;, 
if  present,  water  will  be  deposited  on  the  cool  sides  of  the 
tube. 

MISCELLANEOUS  TESTS. 

Carbonates. — Treated  with  hydrochloric,  nitric,  or  sul- 
phuric acid,  carbonic  acid  gas  escapes  with  effervescence ; 
decomposition  will  sometimes  take  place  if  a  drop  is  put  on 
the  mineral  in  mass;  but  in  some  cases  the  mineral  must  be 
pulverized  ;  in  others  the  application  of  heat  is  necessary. 

Sulphates. — With  few  exceptions,  heated  with  hydro- 
chloric or  nitric  acid  treated  with  a  soluble  salt  of  barium, 
yield  a  white  precipitate  of  barium  sulphate. 

Nitrates: — Heated  on  charcoal  deflagration  takes  place; 
or  better,  heated  in  a  tube  with  powdered  charcoal  deflagra- 
tion occurs. 

Sulphides. — Heated  with  soda  on  charcoal,  moistening 
assay  so  obtained  and  placing  on  a  silver  plate,  the  latter  will 
be  tarnished  if  sulphur  be  present.  The  sulphides  heated 
with  nitric  acid  often  give  a  mass  of  sulphur  floating  on  the 
surface  of  the  acid  ;  sulphides  roasted  in  air  give  a  sulphur- 
ous odor. 


CHAPTER   III. 

DESCRIPTIVE    MINERALOGY. 

NATIVE   ELEMENTS. 

Diamond,  C. 

Isometric. — Commonly  in  octahedrons,  but  often  in  more 
complex  forms,  faces  frequently  curved. 

The  diamond  varies  from  colorless  specimens  through 
various  shades  of  yellow,  orange,  red,  green,  blue,  brown, 
and  sometimes  black.  Transparent  when  white,  dark 
varieties  translucent  to  opaque.  The  luster  is  adamantine  to 
greasy.  H.  =  10.  G.  =  3.516-3.525  in  distinct  crystals. 

Bort  is  a  rounded  variety  of  diamond,  with  rough  exterior 
and  lacking  distinct  crystalline  structure ;  its  hardness  is 
greater  than  the  ordinary  form  (distinct  crystals),  but  its 
specific  gravity  less. 

Carbonado,  or  black  diamond,  is  massive,  but  with  crys- 
talline structure,  sometimes  granular  to  compact ;  its  specific 
gravity  is  sometimes  as  low  as  3.01,  but  it  excels  in  hardness 
all  other  forms.  It  is  found  mainly  in  Brazil. 

The  composition  of  the  diamond  is  essentially  pure 
carbon,  but  the  different  specimens  of  the  gem  which  have 
been  tested  by  combustion  leave  a  small  quantity  of  ash, 
showing  impurity  varying  from  one-twentieth  of  one  per 
cent  to  two  per  cent.  In  this  ash,  silica  and  the  oxide  of 
iron  have  been  detected.  The  black  diamond  leaves  the 
greatest  amount  of  ash. 

The  diamond  heated  to  a  very  high  temperature  with 
the  air  excluded  is  converted  into  a  black  mass  resembling 
graphite  or  coke,  without  loss  of  weight ;  highly  heated  in 
the  air  it  is  completely  oxidized  (except  the  small  quantity 
of  ash)  yielding  CO,. 

32 


UNI  V  ft  ASH' V  OF 

Mf»*TMKMT  or  CIVIL  CNQI  M  cam 

•KRKCLKY,  CALIFORNIA 

NATIVE   ELEMENTS.  33 

The  diamond,  until  the  discovery  of  the  South  African 
fields,  was  found  mainly  in  alluvial  deposits  of  gravel,  sand, 
and  clay,  often  associated  with  gold,  platinum,  quartz,  topaz, 
garnets,  corundum,  tourmaline,  and  other  accessory  miner- 
als. The  frequent  presence  of  itacolumite  in  the  diamond 
regions,  and  the  fact  that  diamonds  have  been  found  in  this 
rock  in  Brazil,  have  led  to  a  rather  general  belief  that  ita- 
columite (flexible  sandstone)  is  the  principal  original 
diamond-bearing  rock.  The  occurrence  of  diamonds  in 
place  in  the  South  African  mines  shows  that  such  is  not  the 
case.  In  these  fields  the  diamonds  are  found  associated  and 
imbedded  in  a  highly  basic,  brecciated  volcanic  rock,  and  it 
is  still  undetermined  whether  the  diamonds  were  present  in 
the  original  rock  from  which  the  breccia  came  .or  whether 
they  were  produced  by  the  action  of  the  volcanic  products 
upon  the  carbonaceous  material  which  is  found  in  the  region 
as  shale.  Prof.  H.  C.  Lewis,  who  gave  able  consideration 
to  the  subject,  advocated  the  latter  theory. 

The  South  African  mines  have  yielded  more  diamonds 
than  all  the  previous  production  of  the  world.  Ninety-five 
per  cent  of  the  world's  yearly  supply  of  diamonds  is  now 
obtained  from  these  mines,  the  remainder  coming  almost 
entirely  from  Brazil,  India,  and  Borneo.  A  few  diamonds 
have  been  found  in  the  United  States  and  Australia ;  those 
obtained  in  this  country  have  been  found  mainly  in  the 
Southern  Alleghanies  from  Virginia  to  Georgia,  or  in  the 
Sierra  Nevada  or  Cascade  ranges  in  Northern  California 
and  Oregon. 

Graphite,  Plumbago,  Black  Lead. 

Hexagonal — In  six-sided  laminge,  commonly  imbedded  in 
foliated  masses.  Granular  to  compact  and  earthy. 

Graphite  is  carbon  with  from  one  to  five  per  cent  ot 
mechanical  impurities,  generally  oxides  of  iron,  manganese, 
and  silicon.  It  varies  in  color  from  iron-black  to  steel-gray  ; 
streak  black,  shining;  luster  metallic.  H.=  i  to  2.  G.  —  2.2^. 
Makes  dark  streak  on  paper  and  has  greasy  feel.  It  is  infu- 


34  DESCRIPTIVE  MINERALOGY. 

sible  both  alone  and  with  reagents  and  is  not  acted  upon  by 
acids.  Combustible  only  at  very  high  temperature.  Defla- 
grates  when  thoroughly  mixed  with  niter  and  heated  in  a 
closed  tube.  In  appearance  greatly  resembles  molybdenite 
(MoS),  but  this  gives  off  sulphurous  fumes  before  the  blow- 
pipe and  is  acted  upon  by  nitric  acid. 

Graphite  occurs  as  scales  and  grains,  nodular  masses,, 
and  in  beds,  generally  in  the  crystalline  rocks.  It  is  found 
in  New  York,  Pennsylvania,  Massachusetts,  Connecticut,, 
Rhode  Island,  New  Jersey,  North  Carolina,  South  Carolina, 
Colorado,  and  California,  and  in  several  other  states.  It  has, 
been  mined  in  New  York,  Massachusetts,  Connecticut* 
California,  and  North  Carolina.  The  Ticonderoga  mine  in. 
New  York  and  the  Herron  mine  in  North  Carolina  are  the 
most  important. 

Ceylon,  Bavaria,  and  Siberia  supply  most  of  the  foreign- 
graphite  and  much  that  is  used  in  this  country  also.  The 
English  deposit  at  Borrowdale  long  furnished  a  superior 
quality  of  graphite,  but  is  now  nearly  worked  out. 

Graphite  is  largely  used  for  the  manufacture  of  lead- 
pencils,  being  ground  up,  and  generally  mixed  with  some 
cementing  material  and  solidified  by  pressure.  Fine  clay  is. 
used  in  the  harder  pencils.  It  is  also  largely  used  as  a  lubri- 
cant for  machinery,  for  coating  objects  to  be  electrotyped, 
for  polishing  stoves  and  other  iron- work,  as  a  paint  for 
smokestacks,  boilers,  etc.,  and  for  making  crucibles ;  for  the- 
latter  purpose  being  mixed  with  clay. 

Native  Sulphur,  St 

Orthorhombic. — Most  common  form,  right  rhombic  acute 
octahedron.  Also  various  modifications  of  this  form,  and 
massive. 

Sulphur  when  pure  is  of  a  clear  yellow  color,  frequently 
somewhat  translucent,  but  sometimes  opaque.  Its  streak  is. 
yellow,  sometimes  tinged  reddish  or  greenish ;  it  is  very 
fragile  and  breaks  with  conchoidal  fracture,  vitreous  or- 
resinous  luster.  G.  =  2.1.  H.  =  1.5  to  2.5.  Readily  combusr- 


NATIVE   ELEMENTS.  35 

tible,  burning  with  blue  flame  and  producing  suffocating, 
acrid  fumes.  In  closed  tube  wholly  volatilizes  and  deposits 
on  cool  part  of  tube. 

The  native  form  is  most  generally  met  with  as  masses  or 
small  grains  disseminated  in  other  minerals,  or  as  fine  yellow 
powder  lining  cavities.  It  often  contains  clay  or  bitumen 
and  is  sometimes  colored  orange-yellow  by  selenium  sul- 
phide. The  largest  deposits  of  sulphur  are  found  in  recent 
sedimentary  strata  associated  with  gypsum  or  allied  rocks, 
or  in  regions  of  extinct  or  active  volcanoes  ;  nearly  all  active 
volcanic  regions  yield  it  in  some  abundance.  The  greater 
proportion  of  the  supply  of  native  sulphur  is  obtained  from 
the  volcanic  districts  of  Sicily.  It  is  usually  purified  from 
earthy  impurities  by  fusion  before  shipment  to  the  world's 
market. 

Sulphur  deposits  are  found  in  many  places  in  the  United 
States  both  in  the  East  and  the  West.  Those  in  the  Eastern 
States  are  too  small  to  be  of  industrial  importance  except  cer- 
tain beds  in  Louisiana,  which  are,  in  places,  over  one  hundred 
feet  thick  and  contain  a  large  quantity  of  pure  sulphur,  but 
they  are  four  or  five  hundred  feet  below  the  surface.  The 
difficulty  of  mining  these  deposits  has  thus  far  proven  so 
great  that  they  have  yielded  only  a  small  quantity  of  sul- 
phur. Deposits  in  the  West  are  numerous  and  occur  in  Cali- 
fornia, Nevada,  Utah,  Wyoming,  New  Mexico,  and  Arizona 
Those  most  important  as  a  source  of  sulphur  are  at  the  Rab- 
bit Hole  mines,  in  Humbolt  County,  N.  W.  Nevada.  These 
at  the  present  time  furnish  the  greater  proportion  of  the 
sulphur  mined  in  the  United  States.  The  mines  near 
Beaver,  Utah,  are  next  most  productive.  Sulphur  is  very 
generally  deposited  around  springs  whose  waters  contain 
hydrogen  sulphide  in  solution,  especially  in  volcanic  regions. 
Immense  deposits  of  sulphur  are  known  to  exist  in  the  crater 
of  Popocatepetl.  The  sulphur  consumed  in  the  United 
States  comes  mainly  from  Sicily,  which  also  furnishes  the. 
greater  proportion  of  the  world's  supply. 


36  DESCRIPTIVE  MINERALOGY. 

Native  Gold. 

Isometric. — Octahedrons  and  dodecahedrons,  but  these 
are  rarely  found. 

Gold  has  a  yellow  color  in  mass,  but  when  reduced  to 
very  fine  powder  it  is  ruby-red.  It  is  very  ductile  and  mal- 
leable. H.  =  2.5  to  3,  nearly  as  soft  as  lead.  G.  =  19  to  19.3. 
Fusing-point  slightly  above  2000°  F.  Not  acted  upon  by 
any  of  the  common  acids ;  dissolved  by  nitro-muriatic  acid ; 
does  not  oxidize  in  the  air. 

Gold  is  seldom  found  pure.  It  is  most  commonly  alloyed 
'with  silver,  sometimes  with  copper,  iron,  rhodium,  and  bis- 
muth. It  is  occasionally  found  combined  with  tellurium. 
The  silver  present  in  the  gold  varies  from  a  fraction  of  a 
per  cent  to  one-third  of  the  whole.  An  amalgam  of  gold 
•and  mercury  has  been  found  in  Colombia,  S.  A.,  and  in  Col- 
orado. The  native  gold  of  California  averages  about  88  per 
•cent  of  gold,  the  remainder  being  mostly  silver.  The  native 
alloys  with  silver  are  much  lighter  in  color  than  gold  and 
occasionally  nearly  silver-white. 

Iron  and  copper  pyrites  may  closely  resemble  gold  in 
color  and  have,  by  the  inexperienced,  been  mistaken  for  it ; 
for  this  reason  they  are  sometimes  called  "fools  gold." 
These  minerals  are  brittle  and  give  off  sulphurous  fumes 
when  roasted  in  the  air,  which  at  once  distinguish  them  from 
gold. 

Gold  occurs  principally  in  two  ways:  i.  In  quartz  veins 
intersecting  metamorphic  rocks,  frequently  associated  with 
ores  of  other  metals.  2.  As  grains  and  nodules  in  the  gravel 
and  sands  of  the  rivers  and  valleys  of  auriferous  regions. 
The  deposits  in  the  second  case  result  from  degradation  of 
the  veins.  The  quartz  veins  most  commonly  occur  inter- 
secting metamorphic  talcose,  chloritic  and  argillaceous 
schists,  less  frequently  in  diorites  and  porphyries. 

The  gold  occurs  irregularly  distributed  throughout  the 
quartz  of  the  vein,  in  strings,  scales,  and  grains,  and  is  often 
invisible  to  the  naked  eye.  The  most  perfect  crystals  and 
largest  masses  generally  occur  in  the  cavities  of  the  quartz. 


NATIVE  ELEMENTS.  37 

The  most  common  minerals  accompanying  the  gold  in  the 
vein-stuff  are  the  sulphides  of  iron,  copper,  lead,  and  zinc 
and  the  red  oxide  of  iron.  The  iron  pyrite  exceeds  in  quan- 
tity all  the  other  minerals  and  is  usually  auriferous,  the 
others  frequently  so. 

The  quartz  of  the  veins,  for  some  distance  below  the  sur- 
face, is  often  cellular  and  porous  owing  to  the  alteration  and 
removal  of  the  associated  minerals  by  atmospheric  agencies. 
The  gold  that  was  present  in  the  removed  mineral  is  thus 
frequently  left  in  strings  or  scales  in  the  cavities  of  the 
quartz.  This  weathered  portion  of  the  vein  is  more  easily 
mined  and  the  gold  more  easily  obtained  from  it  than  from 
the  unchanged  portion.  In  quartz  mining  the  gold  is  either 
obtained  from  the  quartz  or  from  the  associated  minerals  ; 
the  pyrite  of  a  gold  region  is  often  worked  as  a  gold  ore,  as 
is  also  the  galenite. 

The  method  of  obtaining  the  gold  from  the  sands  and 
gravels  constitutes  "alluvial  washing";  in  California  called 
placer  mining.  The  origin  of  these  deposits  is  given  in 
Geology.  The  gold  is  obtained  from  the  deposits  by  taking 
advantage  of  its  great  specific  gravity,  the  earthy  matter 
being  washed  away  by  water.  At  first  this  was  accom- 
plished by  simple  pan  or  cradle  washing,  but  soon  in  Cali- 
fornia it  developed  into  hydraulic  mining  upon  a  stupendous 
scale  ;  water  for  this  purpose  being  often  brought  from  long 
distances  by  artificial  channels  and  turned,  under  great 
pressure,  on  the  gravel-beds.  Large  bodies  of  sand  could 
by  this  means  be  washed  over;  only  by  such  means 
would  it  have  been  possible  profitably  to  work  immense 
beds  of  comparatively  ppor  material.  The  most  imposing 
beds  of  sand  and  gravel  disintegrate  and  melt  away  under 
the  enormous  force,  aided  by  the  softening  power  of  the 
water. 

The  cost  of  handling  a  cubic  yard  of  auriferous  gravel 
by  the  best  method  of  washing  employed  in  1852  was  re- 
duced more  than  fifty  times  by  the  introduction  of  the 
California  hydraulic  process,  and  as  compared  with  the 
simple  pan-process  the  cost  was  reduced  a  thousand  times. 


38  DESCRIPTIVE   MINERALOGY. 

i 

The  auriferous  beds  thus  washed  over  were  often  from 
one  to  two  hundred  feet  thick.  Up  to  the  present  time 
the  greater  portion  of  the  world's  supply  of  gold  has  come 
from  the  alluvial  washing  and  not  from  the  quartz  minings. 

Gold  is  very  widely  distributed  over  the  globe,  being 
found  to  some  extent  in  nearly  all  countries.  It  occurs  in 
crystalline  or  semi-crystalline  rocks  of  various  ages  from 
the  tertiary  downward. 

Up  to  the  year  1890  the  United  States,  Australia,  and 
Russia  produced  by  far  the  greater  proportion  of  the 
world's  supply  of  gold  ;  since  that  year  the  gold-fields  of 
Africa  have  added  largely  to  the  production.  In  1897  rich 
discoveries  were  reported  on  the  uper  waters  of  the  Yukon, 
but  the  importance  of  the  Klondike  deposit  is  not  yet  fully 
determined. 

Gold  is  mined  in  many  of  the  States  of  the  United  States 
and  also  in  Alaska.  Since  1849,  the  nrs^  year  after  the  dis- 
covery of  gold  in  California,  that  State  has  almost  contin- 
ually led  in  the  production  of  gold.  The  California  pro- 
duction rose  from  five  millions  in  1849  to  sixty  millions  in 
1853.  In  that  year  the  maximum  was  reached.  Between 
1872  and  1878  Nevada  produced  more  gold  than  California, 
as  did  Colorado  in  1897  and  1898.  At  the  present  time 
California,  Colorada,  South  Dakota,  Montana,  Nevada, 
Arizona,  Alaska,  Idaho,  Oregon,  and  Utah  are  our  principal 
producing  regions,  though  many  other  States  are  small  pro- 
ducers. 

The  localities  of  gold-mines  in  the  United  States  are  too 
numerous  to  mention  in  full,  but  they  are  spotted  from  Ala- 
bama to  Labrador  along  the  Appalachians  and  are  numerous 
in  the  Rocky  Mountains  and  along  the  western  slope  of  the 
Sierras ;  the  eastern  slopes  of  the  Sierras  generally  produce 
silver. 

Native  Platinum. 

Isometric. — Native  crystals  rare,  cubes  most  common  ; 
usually  in  grains,  scales,  and  small  masses. 


NATIVE  ELEMENTS.  39 

Pure  platinum  is  nearly  silver-white,  but  the  native  metal 
nearly  steel-gray  ;  streak  same  ;  metallic,  shining  luster ;  duc- 
tile and  malleable.  H.  =4  to  4.5.  G.  =  i6to  19;  when  pure, 
about  21.  It  is  the  most  difficult  metal  to  fuse,  and  is  not 
acted  upon  by  the  common  mineral  acids.  Native  platinum 
is  usually  alloyed  with  one  or  more  of  the  metals  osmium, 
rhodium,  iridium,  palladium,  copper,  and  iron. 

Russia  supplies  much  the  larger  portion  of  the  platinum 
of  commerce.  It  is  found  mainly  in  alluvial  material  in  the 
Ural  Mountains,  near  Goroblagodat.  Brazil,  Borneo,  Co- 
lumbia, and  St.  Domingo  supply  a  small  amount.  It  has  also 
been  found  in  the  United  States  at  several  places,  in  Canada, 
and  in  Australia.  Its  great  use  is  for  the  construction  of 
chemical  and  philosophical  apparatus. 

Native  Silver. 

Isometric. — In  octahedrons  without  apparent  cleavage, 
often  aggregated  into  mossy,  arborescent,  or  filiform  shapes  ; 
occasionally  into  solid  masses. 

Silver  is  white,  often  tarnished  black  by  sulphur. 
Malleable  and  ductile  ;  streak  white  and  shining.  H.  =  2.5. 
G.  =  10.1  to  H.  Fuses  at  about  1900°  F.  It  is  dissolved  by 
nitric  acid,  and  the  solution  gives  a  white  precipitate  by  the 
addition  of  any  soluble  chloride.  The  precipitate  blackens 
in  the  light  and  dissolves  in  solution  of  ammonia. 

Native  silver  is  frequently  alloyed  with  copper,  and 
sometimes  with  bismuth.  It  is  readily  distinguished  from 
tin,  bismuth,  and  other  white  metals  by  its  high  fusing  and 
volatilizing  points,  its  great  malleability,  and  by  the  wet  test 
above  given. 

Native  silver  occurs  in  veins  traversing  metamorphic 
rocks.  It  is  usually  accompanied  by  the  ores  of  silver,  and 
frequently  of  other  metals.  Four-fifths  of  the  product  from 
the  celebrated  mine  of  Kongsberg,  Norway,  was  native 
silver.  This  mine  was  discovered  in  1623,  and  several 
masses  of  silver  weighing  from  100  to  500  pounds  have  been 
taken  from  it. 


40  DESCRIPTIVE  MINERALOGY. 

Silver  is  found  in  the  Lake  Superior  region  penetrating 
the  native  copper.  It  there  exists  in  strings  and  masses, 
and  is  nearly  pure  silver.  It  has  also  been  found  in  similar 
forms  in  the  silver-mines  of  Idaho,  Colorado,  California,  and 
Nevada.  Peru  has  furnished  much  native  silver,  and  much 
has  come  from  Northern  Mexico.  Both  gold  and  silver  are 
present  in  sea-water,  though  to  a  very  small  extent. 


ORES   OF   SILVER. 

Argentite,  Silver  Glance,  Ag3S. 

Isometric. — This  important  ore  of  silver  generally  occurs, 
when  crystalline,  in  some  modification  of  the  dodecahedron, 
also  in  dendritic,  capillary,  and  reticulated  forms,  massive. 

Argentite  has  a  dull  metallic  luster  ;  its  color  on  fresh  sur- 
face is  a  blackish  lead-gray,  streak  similar  to  color,  and 
glistening.  It  is  malleable  and  sectile.  H.  =  2  to  2.5. 
G.  =  7.2  to  7.4.  Fuses  before  the  blowpipe  and  gives  off 
fumes  of  burning  sulphur,  yielding  a  bead  of  silver.  Acted 
upon  by  nitric  acid  with  a  separation  of  sulphur ;  hydro- 
chloric acid  added  to  nitric  acid  solution  gives  precipitate 
of  silver  chloride.  Solution  in  NO3H  deposits  silver  on 
copper  plate.  Silver  sulphide  is  distinguished  from  the  re- 
sembling ores  of  lead  and  copper  by  its  malleability,  by 
yielding  silver  on  charcoal ;  it  is  also  heavier, than  resembling 
copper  ores. 


Pyrargyrite,  Ruby  Silver,  Dark  Red  Silver  Ore,  Ag3SbS3. 

Rhombohedral. — Occurs  in  columnar  crystals,  faces  often 
rounded,  also  massive. 

This  ore  in  thin  fragments  has  a  dark  cochineal  color,  in 
larger  masses  nearly  black,  streak  cochineal  or  brownish 
red ;  fuses  easily  before  the  blowpipe  with  spirting,  giving 
white  coating  of  antimony  oxide,  ultimately  a  bead  of  sil- 
ver. In  open  tube  gives  sulphurous  fumes  and  white 


ORES   OF  SILVER.  4* 

sublimate,  in  closed  tube  red  sublimate.     Decomposed  by 
NO3H,  depositing  sulphur  and  the  sesquioxide  of  antimony. 


Proustite,  or  Light  Red  Silver  Ore. 

This  ore  is  closely  related  to  pyrargyrite,  but  contains 
arsenic,  replacing  the  antimony  in  part  or  whole.  The  streak 
and  color  are  brighter  red  than  in  pyrargyrite.  Heated  in 
air  gives  sulphurous  and  arsenical  fumes,  in  open  tube  white 
sublimate,  in  closed  tube  yellow  orpiment. 


Stephanite,  Black  Silver,  Brittle  Silver  Ore. 

This  ore  is  also  a  sulphide  of  silver  and  antimony,  whose 
composition  is  represented  by  the  formula  AgBSbS4  = 
5Ag.2S,Sb3S3.  It  has  metallic  luster. 

Black  color  and  streak;  is  brittle  and  usually  massive.  In 
the  open  tube  fuses,  giving  off  sulphurous  and  antimonial 
fumes ;  before  the  blowpipe  on  charcoal  fuses  easily,  giving 
a  coating  of  antimony  oxide,  with  soda  a  globule  of  silver. 

Cerargyrite,  Horn  Silver,  AgCl. 

Isometric. — Usually  occurs  massive  or  as  incrustations, 
also  in  cubes  without  cleavage,  rarely  columnar  ;  color  pearl- 
gray  to  greenish  gray  and  occasionally  violet-blue  ;  by  ex- 
posure to  light  color  changes  to  purplish  brown,  nearly 
black.  When  pure  sometimes  colorless.  Luster  waxy,  res- 
inous to  adamantine;  in  many  cases  cuts  and  looks  like  horn. 
H.  =  i  to  1.5.  G.  =  5.5.  Fuses  in  closed  tube  without  de- 
composition, on  charcoal  reduced  to  metallic  silver.  Soluble 
in  ammonia. 

This  is  a  common  ore  and  has  been  extensively  worked 
in  our  Western  mines  and  in  Mexico. 

The  native  metal  furnishes  only  a  small  part  of  the 
world's  supply  of  silver,  the  larger  portion  coming  from  the 
other  ores  of  silver,  the  principal  of  which  are  the  silver 


42  DESCRIPTIVE   MINERALOGY. 

sulphide,  the  sulpharsenides,  sulph-antimonides,  the  chlo- 
rides and  bromides  and  the  mixtures  of  these  with  the  oxides, 
sulphides,  arseniates,  and  carbonates  of  other  metals.  The 
principal  ores  of  the  Comstock  Lode  were  native  silver  and 
gold,  argentite  (silver  sulphide),  and  stephanite  (sulphide  of 
silver  and  antimony).  Two  hundred  and  eighty  millions  in 
silver  and  gold  were  taken  from  this  lode  between  1860  and 
1880.  In  the  celebrated  Ruby  Hill  mine  at  Eureka,  Nev., 
the  silver  occurred  mainly  as  argentite  and  chloride  mixed 
with  limonite,  lead  sulphite  and  sulphate  and  carbonate,  and 
several  other  minerals.  The  most  important  ore  of  the 
Leadville  region  is  auriferous  galena  with  lead  carbonate 
and  silver  chloride.  Native  gold  and  silver  occur  in  the 
ores  at  both  the  places  last  named. 

The  United  States,  Mexico,  and  South  America  have,  up 
to  the  present  time,  furnished  the  greater  portion  of  the 
world's  silver.  For  the  past  dozen  years  the  United  States 
has  furnished  considerably  over  one-third  of  the  world's 
product  of  silver.  During  this  time  the  silver  yield  of  this 
country  has  varied  in  value  from  about  40  to  76  millions  of 
dollars.  Nevada,  Colorado,  Montana,  Utah,  the  Dakotas, 
and  Idaho  have  been  the  principal  contributors. 


Cinnabar,  HgS. 

Cinnabar  generally  occurs  massive  with  slightly  granular 
texture  ;  when  pure,  it  has  a  bright  red  to  brownish-red  color; 
streak  scarlet;  luster  adamantine.  H.  =  2  to  2.5.  G.  =  9  ; 
less  when  impure.  Impure  varieties  often  have  slaty  struc- 
ture with  darker  color;  streak  tending  to  brown.  Other 
impure  varieties  are  of  a  yellowish-red  color,  little  luster,  and 
yellow  streak.  The  hepatic  cinnabar  or  liver  ore  contains 
carbonaceous  matter  and  clay.  Almost  every  variety  shows 
glistening  specks  in  the  mass.  Pure  cinnabar  is  completely 
volatile.  Roasted  in  air  gives  sulphurous  fumes.  Mixed 
with  soda  and  heated  in  closed  tube  is  decomposed  and  de- 
posits globules  of  mercury  on  cool  sides  of  tube.  These 


COPPER.  43 

tests    readily  distinguish    it    from    cuprite    and    other   red 
minerals. 

Cinnabar  is  the  principal  ore  from  which  mercury  is  ob- 
tained. It  usually  occurs  in  veins  associated  with  slates  and 
shales.  At  Bahknut,  in  Southern  Russia,  it  occurs  impreg- 
nating a  bed  of  sandstone,  from  which  considerable  mercury 
is  obtained.  The  principal  other  mines  are  at  Idria  in  Aus- 
tria, Almaden  in  Spain,  and  New  Almaden  in  California. 
Some  mercury  is  also  obtained  from  Borneo,  Mexico,  and 
Servia.  Mines,  not  now  worked,  exist  in  Chili,  Peru,  China 
and  Japan,  and  several  other  countries.  The  Greeks  are^ 
stated  by  Pliny  to  have  obtained  vermilion  from  Spain  in 
700  B.C.  Besides  being  the  chief  ore  of  mercury,  pure 
cinnabar,  under  the  name  of  vermilion,  is  used  as  a 
paint;  for  this  purpose  it  is  almost  wholly  an  artificial 
preparation. 

Metallic  mercury  in  this  country  is  put  up  at  the  mines 
and  transported  in  iron  flasks  weighing  76.5  pounds. 
Thus  expressed,  the  world's  product,  for  the  past  ten 
years,  has  been  between  100,000  and  110,000  flasks,  of 
which  the  United  States  produced  about  one-fourth.  In 
1887  the  product  of  the  United  States  amounted  to  80,000 
flasks. 


Native  Copper. 

Isometric. — In  octahedrons  and  dodecahedrons,  and  modi- 
fied forms.  The  dendritic  forms  are  frequently  composed 
of  aggregations  of  octahedrons. 

Copper  has  a  red  color  and  is  very  ductile  and  tenacious; 
when  rubbed,  emits  a  rather  disagreeable  odor;  luster 
metallic ;  streak  red.  H.  =  2.5  to  3.  G.  =  8.8  to  8.95.  Fuses 
before  the  blowpipe  and  oxidizes  on  surface  in  cooling;  is 
acted  upon  by  nitric  acid,  and  the  solution  gives  a  blue 
color  on  addition  of  solution  of  ammonia. 

Native  copper  is  widely  distributed,  and  often  contains  a 
little  silver.  It  generally  occurs  to  a  greater  or  less  extent 


44  DESCRIPTIVE   MINERALOGY. 

in  connection  with  its  ores,  especially  the  carbonates  and 
sulphides.  Siberia  and  Cornwall  have  furnished  very 
beautiful  cabinet  specimens  ;  Australia  and  the  South  Ameri- 
can countries  afford  it  in  greater  quantity,  Brazil  especially 
having  furnished  some  very  large  masses.  The  Lake 
Superior  region  of  Michigan,  however,  is  the  most  impor- 
tant locality  in  the  world  for  native  copper.  The  metal 
there  occurs  in  layers,  often  called  veins,  distributed  through 
amygdaloid  and  conglomerate  and  also  in  sandstone.  Much 
of  the  copper  contains  a  fraction  of  a  per  cent  of  silver  in- 
timately alloyed.  It  also  very  frequently  contains  scattered 
grains  and  penetrating  threads  of  silver.  This  mixture  of 
copper  and  silver  is  found  in  other  countries,  and  it  has  not 
been  artificially  imitated.  The  copper  in  the  Lake  Superior 
region  is  nearly  all  in  the  native  state,  and  very  large  masses 
have  been  taken  from  the  mines ;  one  weighing  420  tons 
and  containing  copper  of  90  per  cent  purity  was  taken  from 
the  Minnesota  mine  in  1857. 

The  gangue-stone  contains  generally  from  one  to  five  per 
cent  of  copper.  The  mining  operations  of  the  largest  com- 
pany (Hecla  and  Calumet)  are  simple,  consisting  of  crushing 
and  stamping  the  gangue  and  separating  the  metal  by 
difference  of  specific  gravity,  the  sands  being  washed  away 
by  running  water.  The  machinery  for  this  purpose  is  very 
extensive  and  perfectly  adapted.  The  formations  in  which 
the  copper  occurs  are  not  veins  in  any  proper  sense.  They 
are  most  probably  sedimentary  formations  whose  original, 
position  has  been  changed.  The  most  important  ores  of 
copper  are  given  below. 


ORES    OF    COPPER. 

The  ores  of  copper  are  numerous  and  many  of  them  not 
distinctly  defined  in  composition.  Only  the  more  important 
will  be  described. 

The  common  wet  test  for  a  copper  ore  is  to  act  upon  the 
suspected  mineral  with  nitric  acid,  dilute,  and  add  ammonia; 
if  copper  is  present,  a  blue  solution  is  obtained. 


ORES   OF  COPPER.  45 

Chalcopyrite,  Copper  Pyrites,  Copper  and  Iron  Pyrites,  CuFeS.y 

Is  most  commonly  massive.  Has  a  slighly  greenish, 
bronze-yellow  color,  often  iridescent  by  tarnish.  Streak 
and  powder  greenish  black.  H.  =  3.5  to  4.  G.  —  4  to  4.3. 
Heated  in  the  air  before  the  blowpipe  gives  off  sulphurous 
fumes  and  fuses  to  a  magnetic  globule ;  this  globule  powdered 
and  further  heated  on  charcoal  will  reduce  to  a  bead  of 
iron  and  copper.  Chalcopyrite  must  be  well  roasted  before 
it  will  give  the  copper  test  with  nitric  acid  and  ammonia. 

It  sometimes  resembles  native  gold  in  color,  or  again 
iron  pyrite.  It  is  distinguished  from  the  first  by  lack  of 
malleability,  and  from  the  second  by  its  softness,  richer 
yellow  color,  and  its  greenish-black  streak. 

Chalcopyrite  is  the  ore  from  which  the  bulk  of  the 
copper  of  commerce  is  obtained. 

It  occurs  in  veins  intersecting  metamorphic  rocks  and 
occasionally  in  cavities  or  veins  in  unchanged  sedimentary 
rocks.  Its  most  common  associates  are  the  copper  carbon- 
ates and  the  sulphides  of  iron,  lead,  or  zinc. 


Chalcocite,  Copper  Glance,  Vitreous  Copper,  Cu2S. 

Occurs  in  crystals,  but  usually  massive ;  metallic  luster ; 
color  blackish  lead-gray,  often  tarnished  blue  or  green ; 
streak  same  as  color,  often  glistening;  slightly  brittle. 
H.  =  2.5  to  3.  G.  —  3.5  to  5.8.  Easily  fusible  by  blowpipe 
on  charcoal,  giving  sulphurous  fumes  and  leaving  a  globule 
of  copper.  Acted  upon  by  hot  nitric  acid  with  separation 
of  sulphur ;  nitric  acid  solution  deposits  copper  on  iron  sur- 
face ;  gives  the  usual  copper  test. 

The  ore  is  not  generally  found  pure,  a  portion  of  the 
copper  being  often  replaced  by  iron.  It  occurs  in  great 
abundance  and  in  nearly  a  pure  form  in  several  of  the 
Montana  mines.  It  is  also  an  important  ore  in  Arizona, 
Colorado,  and  New  Mexico. 


46  DESCRIPTIVE  MINERALOGY. 


Bornite,  Erubescite,  Variegated  Copper  3(Cu,S,Fe2S3). 

This  in  appearance  is  one  of  the  most  striking  of  the 
copper  ores  when  in  fresh  condition.  It  then  has  a  brilliant 
purplish-brown  color,  but  changes  on  exposure  to  the  air 
to  many  hues  with  varied  iridescence.  When  pure  it  is 
represented  by  the  formula  3(Cu2S,Fe,S9),  which  may  be 
written  Cu,FeS,.  The  proportions  of  the  constituent 
elements  vary  widely  without  materially  affecting  the 
general  appearance  of  the  ore.  Has  metallic  luster;  the 
streak  is  a  dark  grayish  black.  H.  =  3.  G.  =  4.5  to  5.5.  It 
is  an  important  ore  of  the  Butte  mines. 

Before  the  blowpipe  fuses  easily  to  a  black  magnetic 
globule;  this  taken  with  its  peculiar  color  and  brilliant 
iridescence  distinguishes  it  from  chalcocite. 


Tetrahedrite,  Gray  Copper  Ore. 

This  mineral  when  pure  is  a  double  sulphide  of  copper 
and  antimony.  The  antimony  is  frequently  in  part  replaced 
by  arsenic,  and  the  copper  by  iron,  zinc,  silver,  or  lead.  It 
is  an  unimportant  ore  in  this  country  except  when  it 
becomes  rich  in  silver,  and  is  then  valuable  for  the  silver. 
This  argentiferous  form  of  the  ore  is  found  both  in  Mon- 
tana and  Colorado.  The  pure  tetrahedrite  is  represented 
by  the  formula  4Cu,S,SbaS8. 

Tennantite. 

This  mineral  is  essentially  a  sulphide  of  arsensic  and 
copper ;  it  often  contains  antimony  and  graduates  into  the 
tetrahedrite.  It  is  of  no  importance  in  this  country  as  a 
copper  ore. 

Cuprite,  Red  Copper  Ore,  CuaO. 

Isometric. — Prevailing  form  the  octahedron,  also  in  the 
derived  forms. 


ORES   OF  COPPER.  47 

It  occurs  often  massive  and  also  earthy.  Has  different 
tints  of  deep  red,  often  reddish  gray ;  luster  adamantine  or 
semi-metallic,  dull  in  impure  varieties;  streak  brownish  red. 
H.  =  3.5  to  4.  G.  —  5.8  to  6.1.  Heated  on  charcoal,  reduces 
to  metallic  copper.  Frequently  occurs  with  the  other 
copper  ores ;  outer  surface  often  converted  into  carbonate. 
Gives  copper  test  with  nitric  acid  and  ammonia. 


Melaconite,  Black  Copper  Ore,  CuO. 

Found  as  cubes  in  Lake  Superior  copper  region,  but 
generally  in  black  masses  and  botryoidal  concretions  along 
with  other  copper  ores.  Important  ore  in  some  of  the 
mines  of  this  country,  as  in  Tennessee. 

Tenorite  is  another  variety  of  the  same  ore,  found  in  the 
Vesuvian  lavas  and  in  earthy  forms  about  copper  lodes. 


Malachite,  Green  Hydrous  Copper  Carbonate,  CuC03,CuO,HaO. 

Monoclinic. — Crystals  (rare  in  nature)  generally  tabular 
prisms. 

Usually  occurs  in  incrusted  masses  with  reniform, 
botryoidal,  or  mammillary  surfaces  with  fibrous  texture, 
often  showing  concretionary  structure.  Also  compact  or 
earthy.  Color  varies  from  emerald  to  nearly  grass-green. 
Streak  green,  but  generally  lighter  than  mineral.  Luster 
vitreous,  pearly,  or  silky ;  earthy  varieties  have  little  luster. 
H.  =  3.5  to  4.  G.  =  3.7  to  4.  Acted  upon  by  the  common 
mineral  acids  and  gives  the  copper  test  with  nitric  acid  and 
ammonia. 

Malachite  is  generally  associated  with  other  ores  of 
copper;  and  when  in  sufficient  quantity  is  a  very  valuable 
mineral.  The  incrustations  made  by  it  often  have  banded 
shades  of  green  which  give  a  very  pleasing  effect.  It  is 
susceptible  of  a  high  polish  and  is  much  used  in  indoor 
decorations,  making  beautiful  mantels,  table-tops,  vases, 
etc.  It  is  too  soft  for  jewelry,  though  it  is  sometimes 


4  DESCRIPTIVE   MINERALOGY. 

passed  off  as  turquois,  The  mines  of  Siberia  have  given 
the  largest  quantity,  though  it  occurs  in  a  good  many 
countries  to  a  smaller  extent. 

Azurite,  Blue  Hydrous  Copper  Carbonate. 

This  mineral  is  very  similar  to  malachite,  but  the 
color  varies  from  azure-blue  (the  color  of  the  powder) 
to  indigo-blue ;  its  streak  is  also  blue.  These  charac- 
teristics distinguish  it  from  malachite ;  it  fulfills  the  tests 
given  for  that  mineral.  It  is  valuable  when  abundant, 
but  occurs  much  less  abundantly  than  malachite.  Some- 
times used  as  a  pigment,  but  is  not  very  permanent. 
Contains  a  smaller  per  cent  of  copper  than  malachite. 

Chrysocolla,  Hydrous  Copper  Silicate,  CuOSi03,2H20. 

This  is  an  amorphous,  compact  mineral  of  bluish-green 
color ;  sometimes  occurs  in  thin  layers,  as  incrustations ; 
and  as  botryoidal  masses.  H.  =  2  to  4.  G.  =  2  to  2.4. 
Distinguished  from  the  carbonates  by  its  bluish-green 
color  and  no  visible  action  with  acids;  very  frequently 
contains  the  carbonate.  Valuable  as  an  ore  when  abun- 
dant. 

The  world's  product  of  copper  in  1897  was  about 
412,000  tons,  of  which  the  United  States  furnished  more 
than  one-half.  Michigan,  Montana,  and  Arizona  in  that 
year  gave  over  eleven-twelfths  of  the  yield  of  the  United 
States.  Only  in  the  first-named  State  is  the  metal  ob- 
tained in  large  quantity  from  the  native  form,  elsewhere 
it  is  from  the  ores.  The  principal  Montana  ores  are  the 
different  forms  of  copper  sulphide  in  a  siliceous  gangue. 
Much  silver  is  associated  with  the  ores.  The  Arizona 
ores  are  largely  the  oxidized  forms,  though  they  frequently 
change  to  the  sulphides  in  the  lower  reaches  of  the 
veins. 


OKES  OF  LEAD.  49 


ORES    OF   LEAD. 

Lead  rarely  occurs  native,  but  exists  in  many  compounds. 
It  occurs  combined  with  oxygen,  sulphur,  arsenic,  tellurium, 
selenium,  and  as  carbonates,  sulphates,  chromates,  molyb- 
dates,  and  phosphates.  Its  principal  ore  is  the  sulphide. 

Galenite,  Galena,  Lead  Sulphide,  PbS. 

Isometric, — Usually  in  cubes  or  some  of  the  simpler  de- 
rived forms ;  also  granular.  It  has  metallic  luster,  bluish- 
gray  color,  streak  slightly  darker.  H.  —  2.5.  G.  =  7  2  to  7.6. 
Before  the  blowpipe  on  charcoal  it  fuses  readily  and  emits 
sulphurous  fumes,  coats  the  charcoal  with  lead  oxide,  and 
leaves  a  globule  of  lead.  It  is  acted  upon  by  strong  nitric 
acid  with  separation  of  some  sulphur  ;  this  solution  gives 
black  precipitate  with  ammonium  sulphide. 

Galena  is  a  very  widely  distributed  ore.  It  occurs  both 
in  veins  and  in  beds  or  pockets,  and  both  in  metamorphic  and 
unchanged  rocks.  Galena  is  very  frequently  associated  with 
the  sulphides  of  iron,  copper,  zinc,  and  silver.  Some  silver 
sulphide  is  nearly  always  present  in  galena ;  when  the  silver 
becomes  worth  extracting  the  ore  is  called  argentiferous 
galena.  The  argentiferous  galena  generally  has  a  more 
micaceous  appearance  than  the  common  ore.  The  gangue 
in  lead-mines  is  generally  calcite,  quartz,  or  baryta,  and 
sometimes  fluor-spar. 

Abundant  lead-ore  deposits  occur  in  the  States  of  Iowa, 
Wisconsin,  Missouri,  and  Illinois.  None  of  these  deposits 
come  under  the  head  of  true  veins,  but  are  in  sheets  or  beds 
between  the  strata.  The  sheets  are  usually  only  a  few  inches 
thick  and  are  rarely  accompanied  by  gangue  or  true  vein- 
walls.  The  bed-deposits  in  this  region  are  large,  thick 
masses,  as  though  underground  caves  or  chambers  had  been 
filled  by  the  ore.  It  is  probable  that  the  solvent  waters  that 
produced  the  caves  also  deposited  the  mineral  from  solution. 
Casts  of  fossils  in  galena  are  often  found  in  the  region, 


$0  DESCRIPTIVE   MINERALOGY. 

showing  the  aqueous  origin  of  the  ore.  Galena  occurs  in 
true  veins  in  several  of  the  Eastern  States  and  in  many  of  the 
Western.  Of  late  years  the  greater  portion  of  the  lead  pro- 
duced in  the  United  States  has  been  in  connection  with  the 
gold  and  silver  mining  of  the  West,  the  lead  being  a  by- 
product. In  1897  from  this  source  there  were  obtained 
145,000  tons  of  lead,  while  only  about  50,000  were  obtained 
from  other  domestic  sources. 

The  greatest  consumption  of  lead  is  in  the  manufacture 
of  white  lead,  though  large  quantities  are  used  in  making 
pipes,  shot,  and  sheeting.  Galena  is  sometimes  used  for 
glazing  coarse  stoneware,  being  finely  ground,  mixed  with 
other  glaze  material  and  applied  to  the  vessels. 

Cerussite,  White  Lead  Ore,  Lead  Carbonate,  PbCO,. 

Orthorhombic. — Cerussite  occurs  in  orthorhombic  crystals, 
often  compound,  but  more  generally  the  ore  is  found  gran- 
ular compact,  or  in  earthy  masses.  The  crystalline  forms, 
when  pure,  vary  in  color  from  white  to  dark  gray,  almost 
black ;  the  presence  of  copper  gives  blue  or  green  tinge  ; 
streak  uncolored  ;  luster  adamantine,  vitreous  to  resinous, 
and  pearly.  H.  —  3  to  3.5.  G.  =  6.4  to  6.6.  Brittle.  Fuses 
readily  before  blowpipe  and  yields  lead  in  reducing-flame ; 
acted  upon  with  effervescence  by  nitric  acid  ;  in  closed  tube 
it  decrepitates,  loses  CO2,  and  turns  brown  or  yellow. 

The  lead  carbonate  is  a  very  important  ore  at  many 
mines  in  the  Western  States,  especially  in  Colorado,  Utah, 
and  Nevada.  The  carbonate  is  formed  from  galena  by 
meteoric  agencies,  and  in  these  mines  is  generally  found  as 
loose  sand  or  in  compact  lumps  of  a  yellowish  or  brown 
color,  due  to  the  iron  present ;  clusters  of  crystals  are  also 
frequently  present  in  the  compact  masses. 

Anglesite,  Lead  Sulphate. 

This  ore  of  lead  resembles  cerussite  and  often  occurs 
with  it,  both  being  formed  from  the  sulphide.  Its  crystal- 


ORES   OF  ZINC.  51 

line  system  is  the  same  as  that  of  cerussite.  It  fuses  readily, 
and  in  reducing-flame  or  with  soda  yields  metallic  lead. 
It  is  slightly  soluble  in  nitric  acid,  but  no  effervescence 
which  distinguishes  it  from  the  carbonate.  This  ore  gener- 
ally accompanies  cerussite  in  the  mines  of  the  Rocky  Moun- 
tain region. 


ORES   OF   ZINC. 

If  zinc  occurs  native,  it  has  not  been  found  in  any  con- 
siderable quantity.  It  has  been  reported  from  Australia, 
South  Africa,  Colorado,  and  Alabama,  but  satisfactory  infor- 
mation has  not  yet  been  given  in  regard  to  these  finds.  Its 
compounds  are  pretty  widely  distributed ;  they  are  the 
oxides,  sulphides,  carbonates,  and  silicates,  all  of  which  are 
used  for  obtaining  the  metal. 

Sphalerite,  Blende,  ZnS. 

Isometric. — Prevailing  forms,  the  octahedron  and  dodeca- 
hedron and  modifications.  Often  massive  and  sometimes 
fibrous. 

The  color  of  blende  presents  various  shades  of  yellow, 
red,  brown,  and  black;  also  gray  to  white  and  sometimes 
greenish.  Luster  resinous  to  waxy  and  sometimes  semi- 
metallic.  Streak  is  white  to  yellowish  brown.  H.  — 3.5  to  4. 
G.  — 3.9  to  4.2.  The  purer  specimens  will  often  become 
phosphorescent  by  friction  in  the  dark.  The  sulphides  of 
iron,  cadmium,  and  lead  are  often  present  in  it.  It  is  fusible 
with  difficulty  by  the  blowpipe;  heated  in  open  tube  gives 
sulphurous  odor ;  on  charcoal  gives  yellow  coating  which 
turns  white  on  cooling.  It  is  acted  upon  by  hydrochloric 
acid  and  emits  hydrogen  sulphide ;  often  shows  efferves- 
cence. 

This  ore  occurs  in  many  localities  and  in  rocks  of  all 
ages.  The  lead-mines  of  the  Mississippi  valley  afford  it 
abundantly,  as  do  the  zinc-mines  of  Missouri  arid  Kansas. 
By  oxidation  the  ore  is  converted  into  white  vitriol. 


52  DESCRIPTIVE   MINERALOGY. 

Zincite,  ZnO. 

This  ore  generally  occurs  in  tabular  masses  or  dissemi- 
nated grains.  Luster  adamantine  or  semi-metallic  ;  its  color 
varies  from  bright  red  to  dark  or  brown  ;  streak  is  orange- 
yellow.  H.  =4.0  to  4.5.  G.  =  5.6  to  5.8.  Acted  upon  by 
nitric  acid.  Yields  yellow  coating  on  charcoal,  which  turns 
white  on  cooling.  It  is  a  good  ore  of  zinc,  and  is  the  ore  of 
Sussex  County,  N.  J. 

Smithsonite,  Zinc  Carbonate,  ZnC03. 

Rhombohedral. — Smithsonite  seldom  occurs  distinctly  crys- 
tallized ;  generally  botryoidal,  reniform,  or  stalactitic  ;  some- 
times granular  or  loosely  compacted.  This  ore  is  of  light 
color,  but  seldom  white ;  generally  light  gray  or  brownish 
white,  sometimes  shaded  green,  blue,  or  buff ;  streak  uncol- 
ored  ;  luster  vitreous  to  pearly.  Brittle.  H.  =  2  to  4.  G.  =' 
4.2  to  4.5.  It  is  infusible  before  blowpipe  alone  ;  with  soda 
on  charcoal  gives  a  coating  of  zinc  oxide ;  effervesces  in 
acid. 

This  is  a  valuable  ore  of  zinc,  and  is  found  abundantly  in 
the  mines  of  the  Mississippi  valley,  also  in  Pennsylvania. 
It  very  generally  accompanies  galena  and  sphalerite.  Cer- 
tain forms  of  it  are  termed  dry-bone  by  miners.  The  carbon- 
ate in  England  is  often  called  Calamine. 

Calamine,  Hydrous  Zinc  Silicate. 

Orthorhombic. — Crystalline  forms  seldom  distinct.  Cala- 
mine is  a  hydrous  zinc  silicate  and  closely  resembles  the 
carbonate  in  appearance  and  physical  properties.  It  usu- 
ally occurs  associated  with  the  carbonate,  and  is  found  in 
the  localities  named  above  for  that  mineral.  It  gelatinizes, 
but  does  not  effervesce  with  acids.  It  yields  water  in 
closed  tube. 

Willemite,  Zinc  Silicate. 

Hexagonal,  Rhombohedral. — Occurs  in  long  or  short  hexag- 
onal prisms ;  also  in  massive,  granular,  and  rounded  forms. 


IRON.  53 

This  mineral  differs  from  calamine  in  composition  in  being 
anhydrous. 

Willemite  varies  in  color  from  white  and  greenish  yellow 
through  light  to  dark  brown.  Its  streak  is  uncolored ; 
luster  vitreous  or  resinous.  H.  =  5.5.  G.  =  3.9  to  4.2.  It 
fuses  with  difficulty,  and  gelatinizes  with  acids.  Its  com- 
position is  ZnaSiO4 ;  a  part  of  the  zinc  is  sometimes  replaced 
by  manganese.  It  is  frequently  present  with  zincite  and 
franklinite  being  thus  found  in  New  Jersey. 

Native  Iron. 

Isometric. — Generally  massive.  Native  iron  has  gray 
color  and  streak;  it  is  malleable  and  ductile.  H.  =  4.5. 
G.  =  7.3  to  7.8.  Acts  on  magnet. 

Native  iron  is  of  very  limited  occurrence  ;  there  are 
two  varieties,  meteoric  and  telluric.  Meteorites  contain 
native  iron  usually  alloyed  with  nickel  in  considerable 
quantity,  and  small  quantities  of  cobalt  and  copper  are  often 
present.  A  polished  surface  of  meteoric  iron,  when  acted 
upon  by  nitric  acid,  will  frequently  show  triangular  figures 
indicating  a  coarse  octahedral  structure  in  crystallization. 
These  figures  are  called  Wiedmannstadt's  figures,  and 
when  uniform  in  different  specimens  indicate  an  identical 
origin.  Meteoric  iron  often  contains  nodules  of  iron 
monosulphide  and  the  phosphide  of  iron  and  nickel 
(Schreibersite).  Meteorites  have  been  found  in  many 
places  varying  in  size  from  an  ounce  in  weight  up  to 
twenty  tons.  They  are  believed  to  have  a  non-terrestrial 
origin. 

Telluric  iron  is  native  iron  of  terrestrial  origin.  It  is 
found  as  imbedded  particles  or  grains  in  some  basaltic  rocks. 
Masses  have  also  been  found ;  one  weighing  twenty  tons 
was  found  on  Disco  Island,  Greenland,  in  1870.  It  is 
thought  probable  that  this  telluric  iron  has  been  pro- 
duced by  the  reduction  of  the  iron-bearing  minerals  in 
the  passage  of  the  containing  rock  through  carbonaceous, 
strata. 


54  DESCRIPTIVE  MINERALOGY. 


ORES   OF  IRON. 

The  ores  of  iron  are  the  oxides,  carbonates,  and  sul- 
phides. The  oxidized  forms  and  the  silicates  are  very 
widely  distributed  as  the  common  coloring  matter  of  soils. 
The  ores,  when  heated  in  the  reducing  flame  of  a  blow- 
pipe, become  magnetic,  and  when  treated  with  hydrochloric 
acid  give  a  blue  precipitate  on  the  addition  of  potassium 
lerrocyanide. 

Pyrite,  Iron  Pyrites,  FeS2. 

Isometric. — Usually  in  cubes,  faces  frequently  striated  ; 
striae  of  adjoining  faces  are  always  perpendicular  to  each 
other.  Occurs  in  forms  derived  from  cube,  also  in  globular 
nodules  with  radiated  structure. 

Pyrite  has  generally  a  brass-yellow  color,  sometimes 
brownish  by  surface  alteration ;  is  brittle,  and  has  metallic 
luster.  H.  =  6  to  6.5  ;  will  strike  fire  with  steel.  G.  —  4  to  5. 
Streak  is  brownish  black.  Roasted  before  the  blowpipe 
gives  sulphurous  fumes  and  leaves  a  globule  fusible  with  dif- 
ficulty and  attracted  by  the  magnet.  It  resembles  copper 
pyrites,  but  is  of  a  lighter  color,  harder,  and  has  different 
streak.  It  is  readily  distinguished  from  gold  by  its  hardness 
and  brittleness. 

Pyrite  is  one  of  the  most  widely  distributed  of  ores,  but 
is  more  generally  employed  to  obtain  sulphur  than  iron.  It 
occurs  in  rocks  of  all  ages.  In  auriferous  regions  it  often 
contains  gold,  and  is  sometimes  worked  to  obtain  that  metal. 
Owing  to  its  common  occurrence  in  rocks  and  its  change- 
able nature  it  is  one  of  the  chief  natural  causes  of  rock  dis- 
integration. No  stone  containing  it  should  be  used  for 
building  purposes.  The  disintegration  of  the  rock  contain- 
ing it  is  brought  about  by  the  oxidation  of  the  pyrite  and 
the  solution  of  the  resulting  compound.  Other  sulphides 
of  iron  have  the  same  effect  on  the  containing  rock.  Pyrite 
is  used  in  the  manufacture  of  sulphuric  acid,  alum,  green 


ORES    OF  IRON.  55 

vitriol,   and    sulphur ;    occasionally  the    iron   is   extracted. 
Pyrite  is  sometimes  called  mundic  and  fool's  gold  by  miners. 

Pyrrhotite,  Magnetic  Pyrites,  Fe7S8. 

Hexagonal. — The  crystals  of  this  mineral  belong  to  the 
hexagonal  system,  but  well-defined  crystals  are  rare.  It 
usually  occurs  massive  or  disseminated  in  granular  or  scaly 
aggregates. 

Pyrrhotite  is  a  sulphide  of  iron  whose  general  formula 
is  FeMSM  +  I,  in  which  n  may  vary  from  5  to  16;  the  average 
composition  is  accepted  to  be  indicated  by  Fe7S8,  which 
gives  the  percentage  composition  S  =  39.6,  Fe  =  60.4.  Its 
color  is  generally  between  bronze-yellow  and  copper-red  ;  it 
readily  tarnishes  to  a  dull  bronze  ;  streak  grayish  black. 
H.  =  3. 5  to 4.5.  G.  =4.5  to  4.7.  Brittle  and  slightly  mag- 
netic ;  powder  attracted  by  magnet.  Its  color  and  magnetic 
properties  distinguish  it  from  chalcopyrite ;  these  charac- 
ters and  its  inferior  hardness  from  pyrite.  It  is  acted  upon 
by  HC1,  yielding  H3S ;  before  the  blowpipe  on  charcoal 
gives  magnetic  globule. 

Pyrrhotite  is  found  in  small  quantities  at  many  places, 
and  is  sometimes  used  as  an  ore  of  sulphur  in  the  manufacture 
of  sulphuric  acid.  It  is  often  present  in  meteoric  iron, 
though  the  monosulphide  FeS,  troilite,  is  the  principal  sul- 
phide of  meteorites. 

Mispickel,  Arsenopyrite,  Sulpharsenide  of  Iron,  FeAsS. 

Its  color  is  steel-gray  or  tin-white.  Metallic  luster; 
streak  grayish  black.  H.  =  5.5  to  6.  G.  =  6  to  6.4.  It  is 
brittle,  and  the  texture  often  granular,  giving  slightly  hackly 
fracture.  Heated  in  closed  tube  gives  red  and  yellow  sub- 
limates of  arsenic  sulphide  and  also  a  metallic-like  deposit 
of  arsenic;  roasted  before  the  blowpipe  gives  strong  garlic 
odor  of  arsenious  oxide  and  leaves  a  globule  attracted  by 
the  magnet ;  when  struck  sharply  with  a  steel  it  gives  the 
same  odor.  It  is  very  frequently  associated  with  the  ores  of 


56  DESCRIPTIVE  MINERALOGY. 

silver  and  lead  and  the  sulphides  of  iron,  copper,  and  zinc. 
Cobalt  sometimes  replaces  some  of  the  iron  in  mispickel, 
such  compound  being  one  of  the  ores  of  cobalt.  Mispickel 
is  one  of  the  chief  ores  of  arsenic. 


Hematite,  Specular  Iron  Ore,  Fe203. 

Rhombohedral. — Often  in  granular  masses,  compact  or 
friable;  also  lamellar,  micaceous,  and  earthy;  also  in  botry- 
oidal  and  stalactitic  forms. 

The  color  of  the  metallic  varieties  varies  from  iron-black 
to  steel-gray,  the  crystals  often  iridescent.  Luster  metallic, 
of  crystals  brilliant ;  streak  cherry-red  to  brownish  red. 
H.  =  5.5  to  6.5.  G.  —  4.5  to5.3.  Sometimes  slightly  mag- 
netic. The  compact  and  earthy  varieties  have  not  the  luster 
or  color  of  the  metallic,  but  give  the  same  streak.  Acted 
upon  by  hydrochloric  acid,  and  gives  blue  precipitate  upon 
addition  of  potassium  ferrocyanide. 

The  more  important  varieties  of  the  hematite  are  the 
following : 

Specular. — With  distinct  metallic  luster. 

Red  Hematite. — Dark  or  brownish-red  color,  semi-metallic 
luster. 

Micaceous. — In  thin  scales,  schistose  structure. 

Ocherous. — The  red  earthy  varieties  often  containing 
clay  ;  when  soft  and  pulverulent,  red  ocher ;  when  harder, 
compact,  and  of  fine  texture,  it  is  red  chalk. 

Argillaceous. — Includes  compact  red  and  brownish-red 
varieties,  often  of  semi-metallic  luster.  Composed  of  the 
oxide,  with  sand,  clay,  and  often  other  impurities.  The 
most  compact  of  these  varieties,  with  a  jasper-like  texture 
and  appearance,  is  the  jasper  clay  ore.  The  less  hard  and 
jaspery  gives  the  clay  iron-stone  variety.  This  last  name  is 
also  applied  to  the  clayey  siderite  and  limonite. 

When  made  of  flattened  concretions  or  grains  it  is  the 
lenticular  ore.  The  argillaceous  varieties  give  the  red  or 
brownish-red  streak.  When  heated  in  the  reducing-flame 
hematite  easily  becomes  magnetic.  Acted  upon  by  hydro- 


O&ES   OF  IRON.  57 

ch/oric  acid,  and  gives  blue  precipitate  with  potassium 
ferrocyanide.  These  tests,  with  its  red  streak,  serve  to 
distinguish  the  mineral. 

Martite  has  the  same  composition  as  hematite,  but  crys- 
tallizes in  isometric  forms,  octahedrons,  dodecahedrons, 
which  are  thought  to  be  pseudomorphous  of  magnetite ; 
the  color  is  iron-black,  luster  sub-metallic;  the  streak  is 
purplish-brown,  and  the  mineral  but  slightly,  if  at  all,  mag- 
netic. These  characters  distinguish  it  from  magnetite.  It 
is  of  frequent  occurrence  in  magnetic  regions. 

Hematite  is  one  of  the  most  common  and  widely  dis- 
tributed of  ores,  and  occurs  in  rocks  of  all  ages.  It  is  found 
in  so  many  localities  that  only  a  few  can  be  named.  The 
island  of  Elba  has  been  celebrated  for  this  ore  since  before 
the  Christian  era,  and  it  still  produces  it.  The  ore  of  the 
two  so-called  iron  mountains  of  Missouri  was  mainly  hema- 
tite ;  it  is  an  abundant  ore  of  the  Marquette  region,  Michi- 
gan, and  is  found  at  many  other  places  in  the  United 
States ;  when  pure,  it  is  less  easy  to  work  than  the  other 
oxidized  ores. 

The  pulverized  ore  is  used  for  metal  polishing.  The 
artificially  prepared  oxide  furnishes  the  Venetian-red  paint, 
and  the  red  chalk  is  used  for  crayons  and  coarse  pencils. 

Magnetite,  Magnetic  Iron  Ore,  Fe304. 

Isometric. — Prevailing  crystalline  forms  the  octahedron 
and  dodecahedron  ;  very  commonly  massive  and  granular. 

The  color  of  the  ore  is  distinct  iron-black,  luster  semi- 
metallic,  streak  black.  H.  =  5.5  to  6.5.  G.  =  4  to  5.  It  is 
magnetic  and  sometimes  endowed  with  polarity.  Acted 
upon  by  hydrochloric  acid,  and  gives  blue  precipitate  upon 
addition  of  potassium  ferrocyanide.  The  weight,  streak, 
and  magnetic  properties  distinguish  this  ore  from  alj  other 
minerals. 

Magnetite  occurs  in  beds,  principally  in  metamorphic 
rocks,  and  is  most  abundant  in  the  Archean.  It  is  found  in 
many  places  throughout  the  world.  It  is  the  principal  ore 


58  DESCRIPTIVE  MINERALOGY. 

-of  Sweden  and  Norway,  and  exists  in  extensive  beds  in 
New  York  and  to  a  less  extent  in  several  of  the  New  Eng- 
land States. 

Franklinite. 

This  ore  is  similar  to  magnetite,  but  some  of  the  iron  has 
been  replaced  by  zinc  and  manganese.  Its  physical  proper- 
ties  are  about  the  same  as  magnetite,  but  the  streak  is 
generally  not  so  black,  often  a  reddish  brown.  This  ore 
occurs  abundantly  in  New  Jersey  and  often  contains  zincite. 
The  franklinite  is  a  valuable  ore  for  the  manufacture  of  zinc- 
white  and  Spiegeleisen. 


Limonite,  Brown  Hematite,  2Fe203,30H2. 

This  ore  occurs  in  botryoidal,  mammillary,  and  stalac- 
titic  forms  with  fibrous  texture ;  also  massive,  and  as  con- 
cretions and  earthy. 

The  color  is  brown  to  black,  and  in  the  earthy  varieties 
yellowish  brown.  Streak  yellowish  brown.  Luster,  when 
present,  semi-metallic,  sometimes  silky ;  it  is  frequently 
without  luster,  especially  in  the  earthy  forms.  H.  =  5  to  5.5. 
G.  greater  than  4  ;  pulverulent  varieties  less  hard  and  less 
heavy. 

The  principal  forms  of  the  ore  are  the  following : 

Brown  Hematite,  which  includes  the  more  compact  forms, 
usually  with  semi-metallic  luster,  the  botryoidal,  stalac- 
titic,  etc. 

Ocherous  Ore. — All  soft,  earthy  varieties  of  brown  or 
yellowish  color,  giving  the  brown  and  yellow  ochers. 

Impure  compact,  clayey  ores  constitute  the  brown  and 
yellow  clay  iron-stone. 

Bog  Ore  is  a  soft  brownish-black  ore  when  pure.  It 
sometimes  takes  imitative  forms,  and  when  mixed  with  silica, 
which  is  very  frequently  the  case,  is  quite  hard. 

These  ores  give  off  water  in  a  closed  tube  readily,  be- 
come magnetic  before  the  blowpipe,  and  give  the  iron  test 


OKES   OF  IRON.  59 

with  hydrochloric  acid  and  potassium  ferrocyanide.     These 
characters  with  the  streak  distinguish  the  ore. 

Limonite  is  a  common  and  valuable  ore  and  is  abundantly 
and  widely  distributed  in  the  United  States.  The  localities 
of  its  occurrence  are  too  numerous  to  mention.  The  ore  is 
the  result  of  the  alteration  of  iron-bearing  minerals,  brought 
about  by  atmospheric  agencies.  The  yellow  ocher  is  used 
for  a  common  paint.  The  name  limonite  is  from  the  Greek 
word  for  meadow. 

Siderite,  Spathic  Iron  Ore,  Chalybite,  Iron  Carbonate,  FeC03. 

Rhombohedral. — Occurs  also  in  botryoidal  and  nodular 
forms,  in  compact  masses  and  earthy.  Crystalline  form 
shows  sparry  faces  which  are  often  curved. 

Color  of  mineral  is  ash-gray  to  yellowish  gray,  yellow 
to  reddish  brown,  often  brown  to  brownish  black  from 
exposure.  Luster  pearly  to  vitreous,  also  dull.  Streak 
light  yellow  to  yellowish  brown.  H.  — 4.  G.=4.  Before  the 
blowpipe  it  blackens  and  becomes  magnetic.  When  pow- 
dered acted  upon  with  effervescence  by  hydrochloric  acid, 
and  gives  a  blue  precipitate  upon  addition  of  potassium 
ferrocyanide. 

Spathic  Ore  is  the  crystallized  form  with  sparry  faces. 
When  the  ore  is  largely  mixed  with  clay  it  gives  the  clay 
iron-stone,  and  when  bituminous  matter  is  present  it  is  the 
black  band. 

It  is  a  valuable  ore,  occurring  as  the  gangue  in  certain 
veins,  and  in  beds,  and  is  abundant  as  clay  iron-stone  in 
the  coal  formations.  It  takes  the  limonite  color  when 
exposed  to  atmospheric  agencies  due  to  conversion  into 
that  form.  Chalybeate  waters  hold  it  in  solution  and 
deposit  it  upon  coming  to  the  surface,  the  color  around 
such  springs  being  due  to  its  conversion  into  hydrated 
sesquioxide. 

The  clay  iron-stone  constitutes  the  great  ore  of  England. 
It  occurs  also  in  the  coal-beds  of  Pennsylvania,  West  Vir- 
ginia, and  Ohio.  The  United  States  now  produces  more 


6O  DESCRIPTIVE  MINERALOGY. 

iron  than  any  other  country  in  the  world,  England  coming 
next  in  production  with  nearly  as  much. 

Chromite,  Chromic  Iron  Ore,  FeCr204  or  FeOCr203. 

Isometric. — Chromite  usually  occurs  in  granular  or  com- 
pact masses  or  in  disseminated  grains.  Color  is  brownish 
black  to  iron-black  ;  streak  brown.  H.  =  5.5.  G.  —  4.3  to 4.6. 
Sometimes  slightly  magnetic.  It  is  distinguished  from 
magnetite  by  its  streak  and  by  giving  a  green  bead  indic- 
ative of  chromium  when  fused  with  borax. 

Chromite  is  the  source  of  nearly  all  the  compounds  of 
chromium  which  are  so  extensively  used  as  pigments,  its 
principal  use  being  in  the  production  of  potassium  bi- 
chromate. 

Stibnite,  Gray  Antimony,  Antimony  Glance. 

Orthorhombic. — Crystals  prismatic,  long  columnar  or  acicu- 
lar,  faces  vertically  striated ;  pyramidal  faces  curved  or 
distorted  ;  common  in  radiating  or  divergent  groups  of 
acicular  crystals,  also  massive  with  columnar  fibrous 
texture. 

Stibnite  is  the  sesquisulphide  of  antimony,  SbaSt.  Its 
color  is  lead-gray ;  luster  metallic,  very  brilliant  on  fresh 
cleavage  surface ;  tarnishes  black,  sometimes  iridescent ; 
streak  lead-gray.  H.  =  2.  G.  =  4.55  to  4.65. 

Heated  in  open  tube  stibnite  gives  off  sulphurous  and 
antimonial  fumes,  the  latter  being  partly  Sb2O3  and  partly 
Sb2O4 ;  the  first  oxide  is  fusible  and  volatile,  the  latter 
neither.  Stibnite  is  easily  fusible  and  entirely  volatile 
before  the  blowpipe ;  when  pure  it  is  acted  upon  by 
HC1  with  evolution  of  H3S.  The  above  characters  dis- 
tinguish it  from  galena  and  graphite,  which  it  sometimes 
resembles. 

Stibnite  is  the  chief  ore  of  antimony,  besides  being 
directly  used  as  a  substitute  for  sulphur  in  some  prepara- 
tions. 


OXIDES.  6 1 


Pyrolusite,  Black  Oxide  of  Manganese,  Mn02. 

Pyrolusite  occurs  in  orthorhombic  crystals,  but  may  be 
pseudomorphous.  Generally  occurs  in  short  columns,  often 
parallel  fibrous  and  divergent,  granular  massive  and  reni- 
form,  also  compact. 

Pyrolusite  is  the  dioxide  of  manganese,  MnOa.  Its  color 
is  dark  gray  to  iron-black,  sometimes  bluish  ;  luster  almost 
metallic  ;  streak  black.  Crystals  have  a  hardness  of  2  to  2.5, 
other  varieties  softer.  G  =  4.7  to  4.9. 

Fused  with  borax  gives  violet  bead  of  manganese  ;  acted 
upon  by  HC1  with  evolution  of  Cl. 

Pyrolusite  is  the  most  important  ore  of  manganese,  being 
employed  both  for  its  manganese  and  oxygen,  and  for 
making  bleaching-powder. 

Manganite  is  a  hydrous  manganese  sesquioxide.  Its 
streak  is  generally  less  dark  than  that  of  pyrolusite ;  it  is 
also  harder  and  yields  water  in  a  closed  tube. 

Psilomelane  and  wad  are  minerals  largely  composed  of 
oxides  of,  manganese  of  varying  degrees  of  purity,  but  whose 
compositions  are  not  definite. 

Cassiterite,  Tin-stone,  Black  Tin,  Tine  Ore,  Tin  Oxide,  Sn02. 

Tetragonal. — Occurs  in  crystals  of  short  pyramidal  type 
or  slender  columns  acutely  terminated,  twins  common  ;  also 
in  reniform  and  spheroidal  masses  with  divergent  fibrous 
texture  ;  in  granular  masses  and  in  rounded  pebbles. 

The  color  is  sometimes  white,  gray,  yellow,  or  red,  but 
more  generally  brown  or  black  ;  streak  light  gray  to  brown. 
H.  —  6  to  7.  G.  =  6.8  to  7.1.  Before  blowpipe  infusible 
alone,  gives  globule  of  tin  on  charcoal  with  soda. 

Stream-tin  ore  is  the  detritus  from  veins  and  is  found  in 
the  alluvial  deposits  of  streams  which  drain  tin-bearing  re- 
gions. The  globular  masses  of  tin  ore  with  radiating 
fibrous  texture  and  concentric  structure  are  sometimes  called 
wood-tin,  from  the  woody  appearance. 


62  DESCRIPTIVE  MINERALOGY. 

Cassiterite  is  the  principal  ore  of  tin.  It  occurs  in  veins 
intersecting  granite  and  metamorphic  rocks.  The  largest 
amounts  of  tin  are  produced  in  the  island  of  Banca  and  in 
Great  Britain ;  considerable  quantities  also  come  from  Ger- 
many, Austria,  Siberia,  Australia,  and  Bolivia.  Tin  has  as 
yet  been  produced  only  in  very  small  quantity  in  this 
country. 

Rutile. 

Tetragonal. — Often  in  twinned  crystals  ;  in  prisms  of  four, 
eight,  or  more  sides,  faces  of  prisms  usually  striated  verti- 
cally ;  often  in  fibrous  acicular  aggregates  penetrating 
quartz ;  sometimes  massive. 

Rutile  is  the  dioxide  of  titanium,  TiO2.  Its  color  is  red- 
dish brown  to  red,  passing  through  violet,  bluish  to  black, 
sometimes  yellowish  ;  luster  adamantine  or  metallic  ;  streak 
pale  brown.  H.  =  6  to  6.5.  G.  =  4.2  to  4.3. 

It  occurs  in  the  more  distinctly  crystalline  rocks,  both 
metamorphic  and  plutonic. 

It  is  frequently  found  penetrating  quartz  in  acicular 
needles  or  hair-like  fibers ;  polished  stones  of  this  kind  are 
sometimes  very  beautiful  and  constitute  what  the  French 
have  called  "  fleches  d'amour." 


Corundum,  A1203. 

Rhombohedral. — Generally  in  combinations  of  six-sided 
prisms  and  acute  pyramids,  often  with  uneven  and  irregular 
surfaces,  also  massive  and  fine  or  coarse  granular. 

Corundum  is  the  sesquioxide  of  aluminum  ;  the  uncrys- 
tallized  varieties  usually  show  a  small  per  cent  of  iron. 

Corundum  is  sometimes  colorless,  but  generally  some 
shade  of  blue,  red,  or  yellow,  massive  forms  often  brown  or 
black ;  streak  uncolored ;  luster  adamantine  to  vitreous, 
sometimes  pearly  on  bases.  H.  =9.  G.  ==  3.9  to  4.1.  B.B. 
infusible. 

Corundum  is  distinguished  by  its  great  hardness,  infusi- 
bility,  high  specific  gravity,  and  its  luster. 


OXIDES.  6$ 

Sapphire  or  oriental  ruby  are  the  names  applied  to  clear 
crystals  of  fine  colors;  blue  is  the  true  sapphire  color; 
true  ruby  is  red,  highly  prized  as  a  gem. 

Corundum  is  the  name  applied  to  the  dull  irregularly 
colored  crystals  and  masses  as  well  as  to  the  species. 

Emery  includes  the  granular  varieties,  usually  of  dark 
color  from  presence  of  magnetite. 

Corundum,  the  species,  occurs  in  crystalline  rocks,  both 
plutonic  and  metamorphic.  Burmah  and  Ceylon  are  cele- 
brated for  their  rubies  and  sapphires ;  many  fine  gems  have 
been  secured  in  this  country,  the  finds  in  North  Carolina 
and  Montana  being  most  numerous.  Corundum  is  mined  in 
North  Carolina,  and  emery  in  Massachusetts  and  New 
York.  Corundum  and  emery  are  crushed  to  powders  of 
different  fineness  and  used  for  polishing. 

Diaspore  is  the  hydrous  oxide  of  aluminum,  A1,O8,H3O ; 
it  is  usually  found  with  corundum. 


lswft*£ 


Bauxite,  Beau 

Bauxite  is  a  clay-like  mineral  found  also  in  grains,  con- 
cretions, and  massive.  It  is  a  hydrated  aluminum  oxide, 
Al2O3,2HaO;  iron  is  frequently  present,  replacing  some  of 
the  aluminum. 

Its  color  varies  from  white  through  gray  to  yellow  and 
brown  ;  in  its  purer  forms  it  is  largely  used  in  France  in  the 
preparation  of  the  alums  and  also  in  the  manufacture  of 
aluminum. 

Turquois. 

Turquois  is  a  hydrous  aluminum  phosphate.  It  has  a 
bluish-green  color,  vitreous  to  waxy  luster.  H.  =  6.  G.  = 
2.6  to  2.8.  When  heated  before  the  blowpipe  it  gives  off 
water  and  turns  brown ;  infusible,  but  dissolves  quietly  in 
hydrochloric  acid.  It  often  contains  from  one  to  five  per 
cent  of  copper,  also  a  little  iron  and  manganese. 

It  has  been  found  in  New  York,  Arizona,  and  Nevada  in 


64  DESCRIPTIVE  MINERALOGY. 

this  country,  and  in  several  places  abroad.     It  is  susceptible 
of  high  polish  and  is  used  as  a  gem. 


Monazite. 

Monazite  is  a  phosphate  of  the  cerium  group  of  metals. 
It  has  come  into  considerable  prominence  in  the  past  years 
as  the  source  of  cerium  oxide  and  other  infusible  earths.  It 
contains  cerium,  lanthanum,  thorium,  didymium.  It  is  now 
found  in  greatest  quantity  in  rolled  sands  in  Brazil ;  under 
similar  conditions  considerable  quantity  has  been  obtained 
from  North  Carolina. 

Spinel. 

Isometric. — Occurs  only  in  crystals,  usually  in  octa. 
hedrons. 

Spinel  is  an  aluminate  of  magnesium  (MgO,AlaO3)  ;  the 
magnesium  is  often  partly  replaced  by  iron  or  manganese, 
and  the  aluminum  by  iron  or  chromium.  The  color  is 
occasionally  white,  but  more  generally  some  shade  of  red, 
brown,  blue,  or  green  ;  streak  white  ;  luster  vitreous.  H.  = 
8.  G.  =  3. 5  to  4.1.  B.B.  infusible.  Its  most  evident  dis- 
tinctions are  its  hardness,  infusibility,  and  octahedral  form. 

Spinel  occurs  imbedded  in  granular  limestone,  serpen- 
tine, and  other  metamorphic  rocks  ;  also  in  volcanic  rocks. 
The  spinels  of  fine  color  are  prized  as  gems ;  the  red  spinel 
is  the  common  ruby  of  jewelry ;  it  often  resembles  the  true 
ruby  (corundum),  but  the  latter  never  occurs  in  octahedrons. 

Chrysoberyl. 

Orthorhombic. — Occurs  in  short  columnar  or  thick  tabular 
crystals.  Often  forms  compound  crystals,  like  irregular 
six-pointed  stars. 

Chrysoberyl  is  an  aluminate  of  beryllium.  Its  color 
varies  through  several  shades  of  green,  occasionally  rasp- 
berry by  transmitted  light,  pleochroic ;  streak  uncolored  ; 


COMPOUNDS   OF  SODIUM  AND   POTASSIUM.  6$ 

luster   vitreous.     H.  =  8.5.  G.  =  3.5  to  3.8.     B.B.  alone  in- 
fusible. 

Its  hardness,  infusibility,  and  tabular  crystals  and  high 
specific  gravity,  taken  in  connection  with  its  greenish  color, 
are  its  most  evident  characteristics  which  distinguish  it  from 
resembling  minerals. 

Chrysoberyl  is  found  in  this  country  in  Connecticut,Maine, 
New  Hampshire,  and  New  York.  The  finest  crystals  make 
beautiful  gems.  Two  varieties  of  the  species  are  : 

Alexandrite,  which  is  an  emerald-green  chrysoberyl,  sup- 
posed to  be  colored  by  chromium. 

Cat's-eye  has  a  greenish  color  and  exhibits  chatoyant 
effects. 

Halite,  Rock  Salt,  NaCl. 

Isometric. — Cube  the  prevailing  form. 

Rock  salt  is  sometimes  transparent  and  colorless,  though 
often  tinged  some  shade  of  yellow,  red,  or  green.  Its  taste 
is  well  known.  H.  =  2.  G.  —  2.2.  Decrepitates  when  heated, 
easily  fusible,  and  colors  flame  •  yellow.  It  is  soluble  in 
water  and  gives  a  white  precipitate  with  silver  nitrate. 

Salt  exists  in  all  geological  formations  from  the  Silurian 
up.  It  is  found  in  beds  extending  over  large  areas  and  is 
usually  associated  with  gypsum,  anhydrite,  clays,  or  sand- 
stone. In  some  places  the  salt  is  mined,  or  taken  in  the 
solid  state  directly  from  the  beds;  in  others  the  waters 
from  brine-springs  are  evaporated.  The  salt-mines  of  Po- 
land and  Hungary  are  the  most  celebrated  in  the  world. 
The  first,  near  Cracow,  have  been  worked  for  over  seven 
centuries  and  are  almost  of  inexhaustible  extent.  Salt  is 
mined  in  this  country  in  Louisiana,  and  Kansas,  and  in 
Wyoming,  Genessee,  and  Livingston  counties,  New  York. 

Most  of  the  salt  made  in  the  United  States  is  by  the 
evaporation  of  brines  or  waters  from  salt-springs.  Michi- 
gan and  New  York  are  the  chief  producers  by  this  method, 
though  other  States  furnish  some.  The  rock  salt  taken 
from  mines  is  generally  so  impure  that  it  is  dissolved  and 
recrystallized  by  evaporation  before  going  into  the  market. 


66  DESCRIPTIVE  MINERALOGY. 

Salt  is  also  made  in  some  places  by  the  evaporation  of  sea- 
water  or  the  water  of  salt  lakes.  The  consumption  of  salt 
in  the  United  States  is  about  one  bushel  per  capita,  and  the 
productive  capacity  is  considerably  more  than  this. 


Cryolite,  Ice-stone,  Double  Fluoride  of  Sodium  and  Aluminum, 
Na,AlFB  or  3NaF,AlF,. 

Monoclinic. — Cryolite  usually  occurs  massive,  generally 
white,  though  sometimes  giving  shades  from  red  through 
brown  to  black ;  translucent ;  has  an  irregular  platy  or 
fibrous  fracture  which  is  very  characteristic.  It  fuses 
readily  in  forceps,  coloring  flame  yellow  ;  on  charcoal  easily 
yields  clear  bead  ;  acted  upon  by  sulphuric  acid  with  evolu- 
tion of  hydrofluoric  acid. 

This  mineral  is  largely  used  in  the  production  of  alumi- 
num and  formerly  of  sodium.  It  is  principally  obtained  at 
the  Ivigtut  mines  of  west  Greenland,  from  which  place  it  is. 
largely  imported  to  the  United  States. 


Niter,  Saltpeter,  KNO. 

Orthorhombic. — Niter,  when  pure,  is  white  and  very  brit- 
tie.  It  has  a  saline  and  cooling  taste.  H.  =  2.  G.  =  1.97. 
Deflagrates  when  heated  with  powdered  charcoal.  Differs 
from  sodium  nitrate  in  not  deliquescing  when  exposed  to 
the  air. 

Niter  is  sometimes  found  mixed  with  the  earthy  flooring 
of  caves  ;  Kentucky,  Tennessee,  and  several  Western  States 
have  furnished  it  in  small  quantity  from  this  source.  It 
forms  abundantly  as  an  efflorescence  on  the  soil  in  certain 
countries,  especially  during  hot  weather  after  rains.  India 
and  Persia  are  the  most  noted  countries  for  this  natural 
production.  In  many  countries  it  is  artificially  prepared  as 
described  in  Chemistry. 


COMPOUNDS  OF  CALCIUM.  67 


Carnallite. 

Hydrous  chloride  of  potassium  and  magnesium. 

This  mineral  occurs  in  granular  masses.  It  is  of  white 
color  when  pure,  but  generally  reddish  ;  has  a  bitter  taste 
and  is  deliquescent ;  showing  greasy  luster  when  fresh. 

Carnallite  is  found  in  large  quantity  alternating  with 
beds  of  common  salt  at  the  Stassfurt  salt-mines.  It  is  the 
principal  source  of  potassium  chlorid,e. 

Its  composition  is  represented  by  the  formula 

KMgCls,6H,0. 

COMPOUNDS   OF   CALCIUM. 

These  compounds  are  very  abundant  in  the  mineral 
kingdom.  The  most  abundant  and  important  are  the  car- 
bonates, sulphates,  phosphates,  silicates,  and  the  fluoride. 
The  carbonate  is  one  of  the  most  common  of  minerals  ; 
other  native  compounds  are  found  less  commonly.  The 
compounds  named  are  insoluble  or  only  very  slightly  solu- 
ble in  water. 

Fluorite,  Fluor  Spar,  CaF2. 

Isometric. — Prevailing  form  is  the  cube;  also  frequently 
compact  and  fine  granular.  It  is  sometimes  colorless  and 
transparent,  but  usually  has  some  light  color,  e.g.,  some 
tint  of  green,  blue,  purple,  or  yellow  ;  rose-red  and  violet 
shades  are  rare  and  highly  prized.  Streak  light.  H.  =  4* 
G.  =  3.  Below  red  heat  the  mineral  phosphoresces,  but 
above  that  temperature  it  ceases  to  phosphoresce  and  loses 
its  color.  The  phosphorescent  colors  are  independent  of 
the  actual  colors.  That  giving  a  green  phosphorescence 
is  called  chlorophane.  Before  the  blowpipe  the  mineral  de- 
crepitates. It  is  very  brittle. 

Fluorite  occurs  in  veins,  also  in  beds,  and  sometimes  as, 
the  gangue  in  metalliferous  veins,  especially  of  lead  and 


68  DESCRIPTIVE  MINERALOGY 

tin.  It  is  the  most  abundant  native  compound  of  fluorine* 
The  massive  varieties  are  worked  into  vases,  candlesticks, 
and  ornamental  objects.  It  takes  a  high  polish,  but  is  diffi- 
cult to  work  because  of  its  brittleness.  It  is  decomposed 
by  sulphuric  acid,  with  liberation  of  hydrofluoric  acid,  and 
is  used  to  obtain  this  acid  for  etching  on  glass.  It  is  also 
used  as  a  flux  in  certain  metallurgic  operations.  The  Cum- 
berland and  Derbyshire  districts  of  England  are  most  noted 
for  its  production. 

Gypsum,  Hydrous  Calcium  Sulphate,  CaS04,20H2. 

Monoclinic.  —  Crystals  frequently  of  arrow-head  form. 
Occurs  massive  with  foliated  and  granular  texture,  also 
fibrous  and  in  radiating  forms. 

Gypsum  varies  in  color  from  white  to  yellow,  red,  brown, 
and  black.  The  crystals  are  generally  more  or  less  trans- 
parent, other  forms  translucent  to  opaque.  Luster  silky, 
vitreous  to  pearly.  H.  =  2.  G.  =  2.3.  In  thin  plates  flex- 
ible, but  not  elastic.  Before  the  blowpipe  loses  water, 
becomes  white,  opaque,  and  exfoliates.  In  closed  tube  gives 
off  water  easily  ;  dissolves  in  hydrochloric  acid,  and  after 
dilution  gives  a  white  precipitate  with  a  soluble  barium 
salt. 

Gypsum  is  the  most  widely  distributed  of  the  sul- 
phates, and  there  are  several  varieties. 

Alabaster. — This  has  a  very  fine  granular  texture,  almost 
compact  to  the  eye. 

Selenite. — Includes  the  crystalline  forms,  usually  in  trans- 
parent plates. 

Satin  Spar. — A  white,  finely  fibrous  variety.  Some  of 
,  the  fibrous  varieties  have  a  radiated  structure  and  are  then 
called  Radiated  Gypsum. 

Common  Gypsum. — Compact  and  fine  granular,  may  be 
white,  yellow,  brown,  red,  or  black.  Gypsum  occurs  in  ex- 
tensive beds  in  limestone  and  clay  strata.  Common  salt  is  a 
very  frequent  mineral  associate.  When  three-fourths  of  its 
water  is  driven  off  from  gypsum  by  heat  it  constitutes  plaster 


COMPOUNDS  OF  CALCIUM.  69 

of  Paris,  so  called  because  the  gypsum  quarries  near  Paris 
have  long  been  famous  for  supplying  it.  The  plaster  mixed 
with  water  is  used  in  taking  casts,  making  moldings,  etc. 
Alabaster  is  carved  into  various  objects,  as  statuettes,  parlor 
ornaments,  etc.  The  name  of  alabaster  is  sometimes  applied 
to  a  variety  of  calcium  carbonate.  Gypsum,  finely  divided, 
is  also  used  as  a  fertilizer. 


Anhydrite,  CaS04. 

This  mineral  resembles  gypsum,  and  its  tests  are  the 
same  except  that  it  gives  off  no  water  when  heated.  It  is 
also  harder  and  heavier  than  gypsum,  and  its  crystalline 
form  is  orthorhombic.  H.  =  3  to  3.5.  G.  =  3. 


Apatite,  Calcium  Phosphate,  with  Chlorine  and  Fluorine. 

Hexagonal.  —  Prevailing  form  hexagonal  prism ;  also 
massive,  sometimes  globular  with  fibrous  texture. 

Color  is  usually  some  shade  of  green,  but  may  be  white, 
yellow,  reddish  yellow,  or  brown.  Luster  vitreous  to  sub- 
resinous,  streak  light.  H.  =  5.  G.  =  3.2.  It  often  closely 
resembles  beryl  in  appearance,  but  is  softer  and  more  resin- 
ous. It  is  readily  soluble  in  hot  nitric  and  hydrochloric 
acids.  Solutions  treated  with  sulphuric  acid  give  a 
white  precipitate.  Nitric  acid  solution  added  to  molybdate 
of  ammonium  in  excess  gives  immediately,  or  upon  warm- 
ing, a  bright  yellow  precipitate. 

Calcium  phosphate  is  the  main  constituent  of  animal 
bones.  Coprolites  and  guano  are  the  fossil  excrements  of 
birds,  and  are  chiefly  composed  of  calcium  phosphate,  but 
contain  also  the  phosphates  of  ammonium,  sodium,  and  mag- 
nesium. 

Apatite  occurs  in  veins  in  Quebec  and  Ontario,  often  of 
great  purity,  but  generally  mixed  with  rock  material,  such 
as  pyroxene,  hornblende,  calcite,  and  many  others.  Im- 
mense deposits  of  phosphatic  nodules  occur  in  the  Tertiary 
formations  of  South  Carolina  and  Florida.  These  nodules 


7O  DESCRIPTIVE   MINERALOGY. 

contain  from  fifty  to  sixty  per  cent  of  tricalcic  phosphate 
mixed  with  sand,  calcium  carbonate,  and  some  organic 
matter.  The  great  importance  of  guano  and  apatite  is  due 
to  the  phosphoric  acid  in  their  composition.  Both  are  val- 
uable fertilizers.  The  apatite,  before  use,  is  converted  into 
the  soluble  superphosphate  of  calcium  by  treatment  with 
sulphuric  acid.  The  phosphate  industries  of  the  United 
States  are  very  important  and  extensive. 

Calcite,  Calcspar,  CaCOs. 

Rhombohedral. — Often  coarse  and  fine  fibrous,  granular, 
compact,  and  earthy. 

There  are  many  varieties  of  this  mineral,  and  they  vary 
very  much  in  color,  from  transparent  white  to  yellow,  red, 
and  mottled  in  the  crystalline  forms ;  the  compact  forms 
may  be  almost  any  dull  shade  to  black.  Typical  crystals 
have  vitreous  luster,  sometimes  pearly;  fibrous  variety  is 
often  silky  ;  the  others,  from  common  to  earthy  in  appear- 
ance. Hardness  (of  crystals)  3.  G.  =  2.5  to  2.8.  Some  of  the 
earthy  forms  are  very  soft.  Calcite  is  infusible,  but  when 
heated  gives  off  carbon  dioxide  and  is  reduced  to  quick- 
lime, which  when  moistened  gives  alkaline  reaction  ;  it  is 
acted  upon  readily,  with  effervescence,  by  the  mineral 
acids  even  when  cold  ;  the  solution  in  hydrochloric  acid 
diluted  gives  a  white  precipitate  upon  addition  of  sulphuric 
acid. 

Calcite  is  one  of  the  most  abundant  and  widely  distrib- 
uted of  minerals,  probably  coming  next  to  quartz  in  this  re- 
spect. Some  of  the  most  important  varieties  are  mentioned 
below. 

Limestone. — This  term  is  sometimes,  and  not  improperly, 
applied  to  all  calcspars,  but  it  is  generally  limited  to  the 
granular  and  compact  varieties.  The  granular  include  those 
of  a  distinct  crystalline  granular  texture,  often  glistening 
owing  to  the  facets  of  the  grains  ;  architectural  and  statuary 
marbles  are  the  best  examples.  The  latter  must  be  of  fine 
grain,  homogeneous  texture,  and  pure  color.  The  architec- 


COMPOUNDS   OF  CALCIUM.  71 

tural  varieties  may  be  of  various  shades  of  color  and  is  used 
for  decorations  as  well  as  in  structures. 

The  compact  limestones  include  the  crypto- crystalline 
and  non-crystalline  varieties.  Hydraulic  limestone  is  one  of 
these  ;  it  contains  clay  as  an  impurity,  and  produces  a  lime 
that  yields  a  mortar  that  will  set  under  water.  Slow  ef- 
fervescence, conchoidal  fracture,  and  argillaceous  odor  inci- 
cate,  but  do  not  insure,  hydraulic  properties. 

Lithographic  Limestone. — A  very  fine-grained  compact 
limestone ;  its  use  is  indicated  by  the  name. 

Oolitic  Limestone. — Compact  and  often  composed  of  con- 
cretionary grains  somewhat  resembling  the  roe  of  a  fish, 
hence  the  name,  from  the  Greek  oon,  an  egg.  If  the  grains 
are  larger,  the  stone  is  called  pisolite,  from  the  Latin  pisum^ 
a  pea.  The  grains  are  not  always  concretionary,  but  some- 
times comminuted  and  rounded  fragments.  In  each  case 
the  grains  are  cemented  together  by  calcium  carbonate. 

Chalk. — A  compact  but  soft  variety,  mainly  composed  of 
rhizopod  shells. 

Chemically  deposited  Limestone. — Under  this  head  are  in- 
cluded the  limestones  deposited  from  water  holding  them  in 
solution.  Some  of  the  most  important  are:  , 

Travertine. — Deposited  from  rivers  and  springs ;  it  is 
often  in  variegated  layers  and  makes  a  most  ornamental 
marble.  Mexican  onyx  is  an  illustration. 

Stalactites. — The  cones  and  cylinders  found  depending 
from  the  roofs  of  many  caves. 

Stalagmites. — Calcareous  formations  over  the  bottoms  of 
caves  and  often  rising  in  cones,  meeting  similar  projections 
from  above.  These  cave  formations  are  frequently  arranged 
in  different  colored  curved  layers,  and  when  broken  across 
give  very  beautiful  effects.  The  cave  deposits  are  made  by 
the  waters  which  percolate  into  the  caves.  Luray  Cave  in 
Virginia  is  one  of  the  most  celebrated  in  the  world  for  these 
formations. 

Calcareous  Tufa. — An  irregular  porous  deposit  frequently 
incrusting  twigs  or  similar  objects  and  usually  made  by 
small  springs  and  rather  turbulent  waters. 


DESCR 


v  i. 


Rock 
deposited  from  spring 

In  the  case  of  all  t  h 
first  taken  into  solutio  1 
solution,  and  is  depos 
water,  or  in  some  ca  >< 
itself. 

Of  the  non-massiv  •, 
only  necessary  to  mention  a  few  : 

Iceland  Spar. — The  name  applied  to  the  limpid,  crystal- 
line specimens. 

Dog-tooth  Spar. — Composed  of  crystals  of  scalenohedral 
form  ;  frequently  occurs  as  an  incrustation. 

Satin  Spar. — The  delicately  fibrous  variety,  affording  a 
fine  satin  luster  after  polishing. 

In  addition  to  the  varieties  above  described  calcite  occurs 
in  many  other  forms.  The  living  and  often  fossil  shells  of 
the  mollusca  are  mainly  composed  of  it  as  well  as  the  many 
forms  of  shell-limestone  and  coral-rock.  It  is  also  an  essen- 
tial constituent  of  marls.  The  granular  and  compact  lime- 
stones constitute  immense  rock  formations  in  nearly  all  geo- 
logical, ages  and  are  found  widely  distributed.  True  chalk 
is  abundant  in  Europe,  especially  in  England,  but  has  only 
been  found  in  Texas  and  Kansas  in  this  country.  Marble  is 
a  term  applied  to  any  limestone  susceptible  of  a  polish. 
Besides  its  use  in  structures,  limestone  is  the  source  of  quick- 
lime, which  is  employed  in  enormous  quantity  throughout 
the  world  for  making  common  mortar. 


Arragonite,  CaCOs. 

This  mineral  has  the  same  chemical  composition  as  cal~ 
cite,  but  differs  in  crystalline  form,  being  orthorhombic  ;  it 
is  also  slightly  harder  and  heavier.  The  action  under  the 
blowpipe  and  acids  is  the  same  as  that  of  calcite,  except 
that  it  crumbles  to  powder  more  easily  after  heating.  It 
receives  its  name  from  Arragon  in  Spain,  where  very  fine 
crystals  have  been  found. 


COMPOUNDS  OF  CALCIUM.  73; 

Dolomite,  Calcium-magnesium  Carbonate,  Magnesium  Limestone, 

CaMg(CO,)a. 

Rhombohedral. — Granular  and  massive. 

The  massive  varieties  of  dolomite  vary  in  color  from  white 
to  gray,  yellow,  reddish,  green  to  brown  or  black.  The 
lighter  varieties  have  vitreous  or  pearly  luster.  H.  =  3.5  to  4. 
G.  =  2.8  to  2.9,  slightly  harder  and  heavier  than  calcite. 
Before  the  blowpipe  reacts  the  same  as  calcite.  It  gives 
sluggish  effervescence  with  cold  dilute  acid,  sometimes  has 
to  be  powdered  for  this  action.  It  often  cannot  be  distin- 
guished from  calcite  without  a  chemical  analysis. 

Dolomite  is  a  double  carbonate  of  calcium  and  mag- 
nesium and  forms  beds  in  rocks  of  all  ages.  It  occurs 
mainly  in  two  forms  : 

1.  The  distinctly  crystalline  granular  variety,  usually  of 
white  or  yellowish-white  colors,  is  generally  designated  as 
Dolomite.     Its  external  characters  are  often  hard  to  distin- 
guish from  granular  limestone. 

2.  The  finely  granular,  almost  compact  variety  is  gener- 
ally   called   Magnesium   limestone ;    it   is   often    difficult    to 
distinguish  from  siliceous  limestone. 

Dolomite  is  a  common  marble  in  New  York  and  the  New 
England  States,  and  is  largely  used  as  a  building-stone.  It 
is  also  very  common  in  Kansas  and  other  of  the  Western 
States.  Dolomite  is  a  good  building-stone  where  anthracite 
coal  is  the  fuel,  but  in  cities  where  bituminous  coal  is  the 
fuel  the  greater  amount  of  sulphur  present  in  the  coal  is 
found  to  result  very  injuriously  to  the  stone.  This  stone 
was  selected  for  the  new  Houses  of  Parliament  in  London, 
after  the  old  ones  were  destroyed  by  fire  in  1838.  The 
effects  of  the  bituminous  fuel  in  London  have  rendered  it 
necessary  to  protect  the  buildings  by  artificial  preparations 
such  as  soluble  glass,  etc.  Some  of  the  dolomites,  such  as 
the  Sing  Sing  marble,  by  cautious  reduction,  reducing  the 
magnesian  carbonate  with  perhaps  some  (but  not  all)  of  the 
calcium  carbonate,  gives  a  lime  possessing  hydraulic  prop- 
erties. 


74  DESCRIPTIVE  MINERALOGY. 


Witherite,  BaCO,. 

Orthorhombic. — Crystals  nearly  hexagonal  in  form,  like 
modified  hexagonal  pyramids,  but  composed  of  repeated 
twins,  as  shown  by  their  optical  properties,  often  in  com- 
pact aggregates  of  columnar  or  granular  texture. 

Witherite  is  a  barium  carbonate.  Its  color  is  white 
through  gray  to  yellowish ;  luster  vitreous  or  slightly  resin- 
ous ;  streak  white ;  brittle.  H.  =  3  to  3.7.  G.  =  4.25  to  4.35. 
When  heated  in  forceps  gives  yellowish-green  color  to  flame 
and  melts  to  a  clear  glass,  opaque  on  cooling.  Acted  upon 
by  hydrochloric  acid,  effervesces  less  violently  than  calcite ; 
the  solution  gives  white  precipitate  with  sulphuric  acid, 
insoluble  in  acids. 

Witherite  is  used  considerably  in  glass  manufacture,  and 
the  artificial  carbonate  is  used  as  a  poison. 

Quartz,  Silica,  SiOa. 

Hexagonal. — Common  form,  the  hexagonal  prism  with 
corresponding  pyramidal  ends.  Granular,  cryptocrystal- 
line  and  compact. 

Quartz  occurs  under  a  great  variety  of  forms,  but  certain 
properties  are  common  to  them  all.  H.  =  j.  G.  =  2.5  to  2.8. 
Alone  it  is  infusible  before  the  blowpipe,  but  when  heated 
with  sodium  carbonate  it  fuses  with  effervescence,  due  to 
the  escape  of  carbon  dioxide.  It  is  not  acted  upon  by  the 
common  acids  and  shows  no  cleavage.  Quartz  may  be  con- 
veniently divided  into  two  series,  the  distinctly  crystalline 
or  vitreous  series  and  the  cryptocrystalline  or  chalcedonic 
series.  Some  of  the  more  important  varieties  of  each  series 
will  be  briefly  described. 

Crystalline  or   Vitreous  Series. 

The  vitreous  series  have  glassy  luster  and  fracture  and 
include : 

Rock  Crystal. — Which  is  pure  quartz,  colorless,  and  trans- 


SILICA.  75 

parent.  It  is  used  in  jewelry  under  the  name  of  white- 
stone  and  occidental  diamond. 

Amethyst. — Has  a  purple  or  bluish-violet  color;  perfect 
specimens  are  highly  prized.  Color  supposed  due  to 
manganese. 

Rose  Quartz. — Has  rose  color,  which  becomes  paler  after 
long  exposure  to  light.  Usually  occurs  massive,  slightly 
transparent.  Color  probably  due  to  titanic  acid  and 
manganese. 

Smoky  Quartz,  Cairngorm. — Of  a  smoky  or  brownish-black 
tint,  believed  to  be  due  to  organic  matter. 

Milky  Quartz. — Of  a  milky  color  and  sometimes  a  slightly 
greasy  luster,  usually  massive  and  almost  opaque. 

Cat's-eye. — A  gray  or  greenish  variety,  presenting  opa- 
lescence  when  cut  in  convex  form.  Appearance  due  to 
penetrating  asbestos. 

Aventurine. — Aventurine  is  a  form  of  quartz  with  glisten- 
ing spangles,  due  to  the  presence  of  scales  of  mica,  iron 
oxide,  or  other  mineral.  The  basic  color  is  usually  red  or 
brown.  The  aventurine  is  frequently  imitated  in  glass,  but 
such  imitations  can  be  detected  by  the  inferior  hardness. 

There  are  several  other  varieties  of  vitreous  quartz. 
Some  authors  describe  all  the  vitreous  varieties  as  rock 
crystal  more  or  less  pure. 

Cryptocrystalline  or  Chalcedonic  Series. 

Chalcedony. — Waxy  or  horn-like  in  appearance ;  varies 
much  in  color,  generally  translucent ;  frequently  shows  its 
origin  by  deposition  from  siliceous  waters ;  occurs  as  sta- 
lactites, lining  cavities,  and  as  incrustations. 

Agate. — A  mottled  or  cloudy  chalcedony  with  different 
colored  layers  made  by  successive  depositions.  When  a 
section  is  made  across  the  layers  the  colored  edges  are 
shown  in  more  or  less  regular  lines  or  bands.  If  the  layers 
are  very  irregular  the  section  shows  zigzag  lines  and  the 
stone  is  called  fortification  agate. 

An  agate  containing  moss-like  or  dendritic  forms  is  called 


76  DESCRIPTIVE  MINERALOGY. 

moss-agate.  The  colored  layers  are  believed  due  partly  to- 
organic  matter,  partly  to  metallic  oxides  (Fe  and  Mn),  and 
largely  to  rate  of  deposition.  The  colors  of  agates  may  be 
changed  artificially,  and  this  is  sometimes  done  in  agates  cut 
for  ornaments. 

Onyx. — An  agate  with  plane  layers  ;  these  render  it  suited 
for  cutting  into  cameos.  If  the  layers  are  alternately  white 
and  sard,  the  stone  is  a  sardonyx. 

Carnelian. — A  light  red  chalcedony. 

Sard. — A  deep  red  or  brownish-red  chalcedony,  espe- 
cially by  transmitted  light. 

Chrysoprase. — An  apple-green  chalcedony,  colored  by 
nickel  oxide. 

Flint. — A  compact  chalcedony  usually  dark  brown  or 
gray.  It  occurs  in  great  abundance  in  nodular  forms  in 
the  chalk-beds.  It  has  conchoidal  fracture  and  leaves  sharp 
edges  in  breaking. 

Jasper. — An  impure  opaque  chalcedony,  color  some  shade 
of  yellow,  red,  brown,  or  black.  Occasionally  gray  or  green. 
If  in  striped  bands  of  such  colors,  it  is  called  ribbon  or  riband 
jasper. 

Heliotrope  or  Bloodstone. — With  green  color  and  spots 
of  red  ;  the  green  color  is  due  to  some  chlorite,  and  the  red 
to  iron  oxide.  All  the  above  varieties  of  quartz  are  suscept- 
ible of  polish  and  are  used  as  gems  or  in  ornamental  work. 

Granular  Quartz. — In  addition  to  the  above  varieties 
many  rocks  consist  of  silica  nearly  pure,  or  quartz  grains 
firmly  cemented  together  ;  such  are  quartzite  and  quartz 
sandstone.  Buhrstone  is  a  cellular  quartz  rock  having  much 
the  appearance  of  coarse  chalcedony. 

Silica  is  the  most  common  petrifying  material.  It  some- 
times replaces  calcite  and  fluorite  in  their  crystalline  forms, 
thus  giving  pseudomorphous  quartz.  Silica  is  the  common 
petrifying  agent  of  shells  and  wood.  Silicified  wood  is 
found  in  great  abundance  in  Arizona,  Wyoming  (National 
Park),  Colorado,  and  other  Western  States.  The  petrified 
forests  of  Arizona  and  Wyoming  are  very  extensive ;  the 


SILICA.  77 

first  named  have  furnished  specimens  of  agatized  wood  of 
unsurpassed  beauty. 


Tridymite. 

Hexagonal. — This  mineral  is  a  variety  of  silica  whose 
crystalline  form  belongs  to  the  hexagonal  system,  but  it  usu- 
ally occurs  in  minute,  thin  tabular  forms.  The  crystals  are 
generally  minute  and  six-sided,  often  in  twins  or  fan-shaped 
groups.  Its  properties  are  the  same  as  quartz  except  that 
it  is  completely  soluble  in  a  boiling  solution  of  sodium  car- 
bonate. It  occurs  chiefly  filling  cavities  in  acidic  volcanic 
rocks,  often  associated  with  sanidin,  hornblende,  or  augite, 
and  sometimes  opal.  G.  =  2.28  to  2.33. 


Opal 

is  an  amorphous  form  of  silica  containing  from  three  to 
thirteen  per  cent  of  water.  There  are  several  varieties 
differing  widely  in  color.  Opal  is  slightly  less  hard  and 
heavy  than  common  quartz,  has  a  glistening,  resinous  lus- 
ter, and  dissolves  entirely  in  heated  solution  of  potash  ; 
frequently  decrepitates  when  heated.  The  finest  specimens 
give  beautiful  internal  rainbow-reflections  as  the  stone  is 
turned  in  the  light. 

The  luster  and  the  evident  amorphous  texture  usually 
sufficiently  distinguish  opal.  Like  other  silica  it  is  fre- 
quently a  petrifying  material. 

Fiorite,  Siliceous  Sinter.- — These  terms  include  the  siliceous 
incrustations  from  hot  springs ;  they  are  usually  more  or 
less  porous,  sometimes  almost  fibrous. 

Geyser ite. — Includes  the  concretionary  siliceous  deposits 
from  geysers ;  these  deposits  are  very  varied  in  shape,  and 
occur  in  great  beauty  and  abundance  in  the  Yellowstone 
Park.  The  terms  fiorite,  geyserite,  and  siliceous  sinter  are 
very  often  used  synonymously. 

Tripolite,  or  Infusorial  Earth  is  another  form  of  opal  re- 
sulting from  the  accumulation  of  diatom  shells  and  the 


DESCRIPTIVE   MINERALOGY. 


spicules  of    sponges.      The   polishing   powder    known    as 
Electro-  silicon  is  composed  of  this  material. 


SILICATES. 

Silica  is  the  abundant  acid  oxide  of  the  earth's  crust,  and 
forms  silicates  with  various  metallic  bases.  The  silicates  are 
the  most  impotant  rock-making  minerals. 

An  entirely  satisfactory  classification  of  the  silicates, 
based  upon  their  composition,  has  not  been  accomplished, 
as  the  definite  constitution  of  the  acids  from  which  the  sili- 
cates result  is  not  known. 

The  ordinary  classification  of  the  silicates  is  based  upon 
what  appears  to  be  the  ratio  between  the  oxygen  in  the  basic 
and  acid  anhydride  parts  of  the  silicate.  The  principle  of  this 
classification  is  readily  seen  when  the  formulae  of  the  sili- 
cates are  written  after  the  dualistic  method  so  as  to  show 
this  oxygen  relation.  Thus  representing  by  R  a  dyad  me- 
tallic element,  in  the  following  table  are  written  the  gen- 
eral formulae  of  the  silicates  named,  with  the  formulae  of 
the  acids  from  which  they  are  supposed  to  be  formed  : 


.  .  Add. 

Orthosilicate  ........   R2O2.SiO2    I  to  i    SiO4H2    =  SiO2.2H2O  Orthosilicic 

Unisilicates  (Dana) 

Metasilicate  .........  RO.SiO2       ito2   SiO,H2    =SiO2.H2O     Metasilicic 

Bisilicates  (Dana) 

Trisilicate  ...........  2RO.3SiOa  1103   Si3O8H4  =  3SiO22H8O  Trisilicic 

Disilicate  ............   RO.2SiO,     1104   Si,O»H2  =  2SiO2.H2O  Disilicic 

There  are  many  species  in  which  the  oxygen  ratio  is  less 
than  i  :  i,  as  3  14,  2  :  3.  Such  species  are  called  subsilicates, 
and  it  is  evident  that  they  contain  a  larger  proportion  of  the 
basic  radicle  than  the  examples  given  in  the  table.  In  addi- 
tion it  is  thought  probable  that  there  are  other  silicic  acids 
from  which  natural  silicates  may  result.  Neither  can  a  dis- 
tinct line  of  demarcation  be  drawn  between  hydrous  and 
anhvdrous  silicates. 


SILICA  TES.  79 

The  majority  of  the  silicates  come  under  the  head  of 
metasilicates  or  orthosilicates,  and  are  considered  as  derived 
from  the  corresponding-  acids,  SiO,H2,  metasilicic  acid,  and 
SiO4H4,  orthosilicic  acid.  The  normal  orthosilicates  would 
then  be  represented  by  R3SiO4  or  R2O2SiOa,  and  the  normal 
metasilicate  by  RSiO3  or  ROSIO,,  in  which  R  represents  a 
dyad  metal.  When  a  greater  proportion  of  the  acid  or 
basic  radical  is  contained  than  the  formulae  indicate  there 
result  respectively  polysilicates  or  subsilicates.  The  group- 
ing here  adopted  for  the  principal  silicates  is  mainly  in. 
tended  to  emphasize  and  fix  in  mind  their  relationship  and 
importance  as  rock-forming  minerals. 


PYROXENE  AND   AMPHIBOLE   GROUPS. 

The  members  of  these  groups  are  silicates  of  various 
bases,  among  which  generally  appear  calcium,  magnesium, 
andiron;  manganese,  zinc, potassium,  and  sodium  less  often, 
and  aluminum  still  more  rarely.  More  than  one  base  is  usu- 
ally present,  though  some  members  of  the  group  contain  but 
one.  The  two  groups  are  closely  related  in  composition 
and  crystalline  form.  Each  group  shows  forms  belonging 
to  different  systems  of  crystallization,  either  orthorhombic, 
monoclinic,  or  triclinic.  The  monoclinic  species  are  most 
important,  the  triclinic  least  important.  The  amphibole 
group  has  prismatic  cleavage  of  124°  30'  and  55°  30',  while 
that  of  the  pyroxene  group  is  nearly  90°.  This  cleavage 
angle  taken  in  connection  with  the  build  of  the  crystal 
establishes  the  chief  distinction  between  the  groups.  With 
pyroxene  the  distinct  crystals  are  usually  short  prisms, 
often  complex,  in  massive  specimens  lamellar  or  granular ; 
with  amphibole  the  distinct  crystals  are  long  prisms 
and  simple,  in  massive  kinds  columnar  and  fibrous.  Only 
the  more  important  species  of  each  group  are  here  de- 
scribed. 


O  DESCRIPTIVE   MINERALOGY. 

(A)  Pyroxene  Division, 
(i)  Mono  clinic  Section. — Pyroxene. 

Distinct  crystals  usually  in  short  stout  prisms,  often 
complex,  massive,  granular  or  lamellar,  sometimes  fibrous 
or  compact.  The  more  important  varieties  of  this  species 
are  silicates  of  two  or  more  of  the  bases  calcium,  mag- 
nesium, and  iron,  calcium  being  always  present,  with  either 
iron  or  magnesium  or  both  ;  aluminum  in  certain  cases. 
The  color  is  usually  some  shade  of  green,  brown,  or  black; 
also  occurs  white.  Luster  varies  from  dull  vitreous  through 
imperfectly  resinous  to  slightly  pearly.  H.  =  5  to  6.  The 
rectangular  cleavage  when  evident  distinguishes  it  from 
amphibole.  The  more  important  varieties  are  : 

Augite. — This  is  a  very  abundant  and  important  mineral, 
and  is  a  silicate  of  calcium,  magnesium,  iron,  and  aluminum. 
It  is  black  or  greenish  black  in  color  and  opaque.  It  is  the 
common  form  of  pyroxene  in  the  basic  eruptive  rocks.  The 
term  augite  is  sometimes  used  synonymously  with  pyroxene, 
but  more  generally  it  is  limited  to  the  variety  just 
described. 

Diallage  is  a  thinly  foliated  or  lamellar  variety  of  augite. 

Malacolite. — This  is  sometimes  called  white  augite,  and 
is  a  calcium-magnesium  pyroxene.  The  granular  form  is 
frequently  called  white  coccolite,  from  coccos,  a  grain.  The 
green  granular  form,  green  coccolite,  contains  calcium  and 
iron. 

The  varieties  of  the  pyroxene  species  are  very  important 
rock-making  minerals. 

(2)  Orthorhombic  Section. 

The  orthorhombic  pyroxenes  are  magnesium,  or  iron 
and  magnesium,  silicates.  The  species  of  the  pyroxene 
group  under  this  section  are : 

Enstatite. — Which  contains  the  smaller  proportion  of  iron 
oxide — not  over  five  per  cent — and  sometimes  iron  is 
absent.  The  color  varies  from  grayish,  yellowish,  or 


SILICATES.  8  1 

•greenish  white  to  brown.  Luster  vitreous  to  pearly. 
H.  =  5.5.  G.  =  3.1  to  3.3.  It  is  infusible  and  not  attacked  by 
acids  ;  strongly  resembles  the  monoclinic  pyroxenes. 

Enstatite  in  a  very  pure  state  is  a  frequent  constituent 
of  meteorites. 

Bronzite.  —  This  contains  more  iron  than  the  preceding 
and  its  color  deepens  from  grayish  yellow-green  to  olive- 
green.  The  amount  of  iron  oxide  generally  ranges  from 
5  to  14  per  cent  ;  with  a  greater  per  cent  of  iron  the  bronz- 
ite  passes  to  the  next  variety. 

Hypersthene.  —  This  mineral  contains  more  iron  than 
either  of  the  preceding,  the  amount  of  iron  oxide  varying 
from  14  to  30  per  cent.  Color  is  a  dark  greenish  brown  or 
black,  sometimes  approaching  a  copper-red.  Streak  gray 
•or  brownish  gray.  H.  =  5  to  6.  G.  =  3.4  to  3.5. 

Hypersthene  often  has  a  characteristic  iridescence  due 
to  minute,  interspersed  foreign  crystals,  symmetrically  ar- 
ranged. B.B.  it  fuses  to  a  black  enamel,  and  on  charcoal 
yields  a  magnetic  mass.  This  species  is  a  common  constit- 
uent of  certain  of  the  eruptive  rocks. 


,y  ^y^^ 

(i)  Monoclinic  Section.  —  Amphibole. 

The  species  of  the  amphibole  group  form  a  series  closely 
related  to  those  of  the  pyroxene  group  ;  the  general  dis- 
tinction between  the  two  groups  has  already  been  indicated. 
The  amphibole  species  of  this  group  are  analogous  to  the 
pyroxene  species  of  the  pyroxene  group,  being  silicates  of 
the  same  bases,  though  potassium  and  sodium  are  more 
frequently  present. 

Amphibole  usually  occurs  in  columns  less  stout  than 
those  of  pyroxene,  often  in  bladed  crystals,  also  fibrous  and 
granular;  the  cleavage  more  oblique  than  that  of  pyroxene. 
The  color  of  the  amphibole  varies  from  black  to  white 
through  many  shades  of  green  ;  streak  lighter  than  color. 
Luster  vitreous  to  pearly  on  fresh  surfaces,  fibrous  varieties 


82  DESCRIPTIVE  MINERALOGY. 

often  silky.  H.  =  5  to  6.  G.  =  2.9  to  3.4.  The  principal 
varieties  of  this  species  are : 

Tremolite. — A  white  lime-magnesia  amphibole.  It  usually 
occurs  as  blades  or  needles  penetrating  the  gangue  with 
which  they  are  associated,  sometimes  radiated  or  aggregated 
into  columnar  masses  of  silky  luster.  Tremolite  most 
often  occurs  with  dolomite. 

Actinolite. — Of  the  same  composition  as  tremolite  with 
iron  in  addition,  and  occurring  in  the  same  way  as  aggrega- 
tions of  needles  or  blades  or  in  radiating  forms.  It  usually 
occurs  with  serpentine. 

Asbestus. — Both  varieties  of  amphibole  pass  into  asbestus. 
Asbestus  includes  the  finely  fibrous  forms,  fibers  easily 
separable  and  resembling  flax ;  when  the  fibers  are  more 
like  silk  it  is  called  amianthus.  When  the  fibers  adhere 
closely  and  the  stone  resembles  petrified  wood,  it  is  called 
ligniform  asbestus.  When  the  fibers  are  interlaced  so  as  to- 
make  tough  sheets,  it  is  called  mountain  leather. 

Asbestus  is  the  only  variety  of  the  amphibole  species 
used  in  the  arts.  It  is  sometimes  woven  into  lamp-wicks^ 
fire-proof  cloths,  etc.  It  is  incombustible,  and  articles  made 
of  it  may  be  cleansed  by  throwing  them  into  fire.  Asbestus 
is  found  at  many  localities  in  the  United  States,  but  generally 
of  inferior  quality  and  only  adapted  for  grinding,  and  use 
for  paints,  cements,  boiler  and  steam-pipe  coverings,  safe- 
linings,  etc.  The  greater  portion  of  the  mineral  called  as- 
bestus, suitable  for  weaving  into  cloth  is  a  variety  of  serpen- 
tine and  does  not  fall  under  this  species.  Canada  supplies, 
this  serpentine  form  in  large  quantity. 

Crocidolite. — This  species  of  the  amphibole  group  is  a 
silicate  of  iron  and  sodium.  It  occurs  asbestiform,  also- 
massive  and  earthy.  The  color  is  lavender-blue  or  light 
green.  Luster  silky  or  satin  to  dull.  H.  —  4.  G.  =  3. 2  to  3. 3. 
In  closed  tube  gives  a  little  water  which  is  slightly  alkaline. 
B.B.  fuses  easily  with  intumescence  to  a  black  magnetic  glass 
coloring  flame  yellow. 

An  altered  form  of  this  mineral  is  found  abundantly  in 
South  Africa  and  popularly  called  "  tiger-eye  "  or  "  cat's- 


SILICA  TES.  83 

eye."  The  alteration  is  due  to  the  oxidation  of  the  iron  and 
infiltration  of  silica.  The  altered  mineral  has  a  delicate  but 
distinct  fibrous  texture  and  chatoyant  luster,  with  amber- 
yellow  to  brown  color.  This  form  of  the  mineral  has  come 
into  frequent  use  as  an  ornamental  stone. 

Hornblende. — This  term  is  often  used  as  synonymous  with 
amphibole,  but  it  is  more  generally  applied  to  the  dark- 
colored  varieties  containing  a  larger  per  cent  of  iron ;  it 
occurs  in  dark  green  or  black  crystals,  massive  and  com- 
pact. Hornblende,  like  pyroxene,  is  an  important  rock- 
making  mineral.  It  is  an  essential  constituent  of  the 
plutonic  rocks.  Such  difference  as  exists  between  horn- 
blende and  pyroxene  is  probably  mainly  due  to  the  different 
conditions  under  which  they  were  formed,  the  composition 
being  substantially  the  same. 

Chrysolite,  Olivine,  Peridot. 

Chrysolite  is  the  most  important  species  of  a  group 
of  silicates  of  the  same  name.  It  is  an  iron  and  magnesium 
silicate,  color  usually  olive-green,  but  has  different  shades 
passing  to  a  yellowish  brown  or  red ;  streak  uncolored, 
sometimes  yellowish  or  brownish.  Hardness  is  about  the 
same  as  quartz. 

Olivine  is  the  most  common  variety  of  chrysolite ;  it  has 
a  dark  olive-green  or  yellow-green  color.  It  occurs  very 
generally  disseminated  through  basaltic  rock,  sometimes  in 
masses. 

Beryl,  Emerald. 

Hexagonal. — Prevailing  form  hexagonal  prism,  sometimes 
massive. 

Beryl  is  essentially  a  silicate  of  aluminum  and  beryllium 
(glucinum).  There  are  several  varieties  of  this  mineral ; 
some  are  pellucid,  but  they  are  generally  some  shade  of 
yellow,  green,  or  blue.  Luster  vitreous  to  resinous,  streak 
uncolored.  H. =7.5  to  8.  G.= 2.67  to  2.76.  Infusible,  though 
it  changes  color  under  the  blowpipe.  The  common  vari- 


84  DESCRIPTIVE   MINERALOGY. 

eties  with  less  delicate  shades  of  color  are  all  included 
under  the  name  of  Beryl  simply  ;  color  supposed  to  be  due 
to  iron  oxide.  Emerald  is  of  a  rich  green  color  ;  it  contains 
a  small  per  cent  of  chromium  oxide,  to  which  its  color  is 
generally  ascribed.  Aquamarine  includes  the  transparent 
forms  of  very  delicate  shades  of  green  or  blue. 

Fine  specimens  of  beryl  come  from  Siberia,  Ceylon, 
Colombia,  and  Brazil ;  they  have  also  been  found  at  many 
places  in  the  United  States — in  Maine,  New  Hampshire,  and 
North  Carolina,  and  several  of  the  Western  States.  Very 
large  ones  have  been  obtained  in  the  two  States  first  named. 
Beryl  in  color  and  form  often  resembles  apatite,  but  is  much 
harder. 

Garnet. 

Isometric. — Prevailing  forms  are  the  dodecahedron  and 
trapezohedron.  Also  occurs  massive  and  granular. 

Garnet  is  a  cornplex  silicate  which  may  contain  two  or 
more  of  the  metals  calcium,  magnesium,  aluminum,  iron, 
and  chromium,  the  varieties  being  due  to  the  different  pro- 
portions of  these  elements.  Garnets  vary  much  in  color. 
Luster  vitreous  to  resinous.  H.=6.$  to  7.5.  G.  =  3.i  to  4.3. 
The  darker  varieties  may  be  fused  without  difficulty.  The 
more  important  and  common  forms  are  the  following  : 

Almandite,  or  Almandine. — Various  shades  of  light  red  to 
brown.  Those  with  clear  color  and  considerable  transpar- 
ency are  the  precious  garnets.  Almandite  is  an  iron-alumina 
garnet. 

Essonite,  or  Cinnamon-stone. — An  alumina-lime  garnet  of  a 
cinnamon  color. 

Pyrope. — An  alumina-magnesia  garnet  of  a  deeper  red 
color  than  almandine,  sometimes  almost  black.  It  is  also 
called  precious  garnet  when  it  is  fairly  transparent  and  has  a 
pure  color.  Pyrope  is  frequently  found  in  small  rounded 
masses  and  grains. 

Colophonite. — A  lime-iron  garnet,  consisting  of  a  mass  of 
grains  of  a  brownish-red  to  brownish-yellow  color ;  has 
resinous  luster  and  generally  gives  iridescence  when  turned 
in  the  light. 


SILICATES.  85 

The  different  forms  of  garnet  often  occur  disseminated 
through  metamorphic  rocks;  are  found  in  the  gneiss  rocks 
about  West  Point.  In  this  class  of  rocks  the  garnets  are 
usually  almandine.  The  fine  red  garnets  constitute  the 
carbuncle  of  the  ancients. 

Garnets  are  found  at  many  places.  Ceylon  is  noted  for 
its  red  garnets,  but  the  richest  gems  come  from  Burmah. 
Garnets  are  found  at  many  places  in  the  United  States. 
Fine  specimens  of  pyrope  abound  in  Arizona,  New  Mexico, 
Colorado,  and  other  Western  States,  and  are  the  so-called 
Arizona  rubies. 

Lapis  Lazuli. 

Isometric. — Usually  massive.  This  mineral  is  a  com- 
plex silicate  of  aluminum  and  sodium  and  contains  copper, 
iron,  snlphur,  and  chlorine.  It  has  an  azure-blue  color  and 
vitreous  luster.  Its  color  is  thought  to  be  due  to  sodium 
sulphide.  When  powdered  it  is  dissolved  by  hydrochloric 
acid  with  separation  of  gelatinous  silica.  The  finest  speci- 
mens are  much  esteemed  for  making  ornaments  and  for 
inlaid  work.  The  powdered  mineral  was  formerly  used  as  a 
paint  under  the  name  of  ultramarine  ;  this  color  is  now  pre- 
pared artificially,  and  is  very  much  cheaper  than  the  natural 
paint. 

Mica. 

This    term    embraces  a   group    of   minerals   which   are 
essentially  hydrous    silicates    of   aluminum   and    an    alkali 
metal.     Potassium  is  the  alkali  metal  most  abundantly  and 
commonly  present.     Sodium  is  often  present,  and  in    one 
variety  it  entirely  replaces  the  potassium.     The  next  most 
important  constituents  are  lithium,  iron,   and  magnesium, 
the  last-named  metal  being  so  abundant  in  some   varieties, 
that  they  are  sometimes  called  magnesian  micas;  in  these,, 
however,  potassium  is  present.     Most  of  the  micas  contain 
fluorine.     The  formulas  for  the  different  varieties  of  mica, 
have  not  been  precisely  determined. 

The   micas   belong  to  the   monoclinic  system   and   are,- 


86  DESCRIPTIVE  MINERALOGY. 

characterized  by  a  highly  laminated  structure  and  perfect 
cleavage.  The  laminae  are  flexible  and  elastic. 

Muscovite  is  one  of  the  common  micas,  being  a  hydrous 
silicate  of  aluminum,  potassium,  and  iron.  It  has  white  or 
silvery  color,  passing  to  various  shades  of  yellow,  brown, 
and  green.  H.  =  2  to  2.5.  It  is  a  common  constituent  of 
granite,  gneiss,  and  mica  schist,  and  in  these  rocks  usually 
occurs  in  minute  silvery  scales. 

Lepidolite  is  muscovite  containing  a  little  lithium,  which 
gives  it  a  delicate  lilac  or  rose-colored  shade  found  only  in 
this  variety. 

Biotite. — Like  muscovite,  a  hydrous  silicate  of  aluminum, 
potassium,  and  iron,  but  in  addition  containing  a  large  per 
cent  of  magnesium.  It  is  generally  greenish  black  to  black 
in  color.  It  is  even  more  common  in  the  granitic  arid  met- 
amorphic  rocks. 

Mica,  in  the  clear  transparent  forms,  has  long  been  used 
for  furnace  and  stove  doors  and  lamp-protectors.  It  is  now 
very  largely  used  as  an  insulator  in  the  construction  of 
dynamo  machines.  For  this  purpose  the  color  is  imma- 
terial, but  perfect  cleavage  is  necessary,  as  the  plates  must 
be  of  uniform  thickness  and  often  very  thin.  For  insulating 
purposes  small  laminae  can  be  fastened  together  by  suitable 
mucilage  so  as  to  form  large  sheets.  Mica  is  also  ground 
up  and  used  for  mural  painting  and  in  the  manufacture  of 
wall-paper.  It  can  thus  be  made  to  produce  a  metallic, 
frosted,  or  spangled  surface.  The  ground  mica  is  also  used 
as  an  absorbent  of  nitroglycerin  in  certain  mica  powders. 
For  grinding,  waste  mica  is  generally  used.  Mica  is  chiefly 
mined  in  this  country  in  New  Hampshire,  North  Carolina, 
and  South  Dakota.  Most  of  that  now  used  in  this  country 
is  imported  from  India  and  Canada,  though  this  will  proba- 
bly not  be  long  done. 

FELDSPAR. 

The  feldspars  are  essentially  silicates  of  aluminum,  potas- 
sium, sodium,  and  calcium.  They  all  contain  aluminum,  the 
other  metals  alternating  in  the  different  species.  The  com- 


SILICA  TES.  87 

mon  and  important  forms  of  feldspar  all  belong-  to  the  tri- 
clinic  system,  except  orthoclase,  which  is  monoclinic.  The 
group  has  a  hardness  of  from  6  to  7,  and  a  specific  gravity 
of  from  2.4  to  2.7. 


Orthoclase,  Common  Feldspar,  Potash  Feldspar. 

Monoclinic. — Prevailing  forms,  oblique  prisms  or  deriva- 
tives. Also  massive,  with  lamellar  or  granular  texture. 
Sometimes  finely  compact. 

A  silicate  of  aluminum  and  potassium  containing  a 
little  sodium.  Generally  light  or  flesh  color,  though  dark 
colors  are  not  uncommon,  and  there  are  various  intermedi- 
ate shades.  It  is  similar  in  other  respects  to  albite,  except 
that  it  has  two  cleavage  planes  at  right  angles  to  each  other, 
which,  when  evident,  is  sufficient  to  distinguish  it  from  that 
form.  It  is  a  common  constituent  of  many  of  the  igneous 
and  metamorphic  rocks  ;  abundant  in  the  gneiss  about  West 
Point.  Ground  orthoclase  is  extensively  used'  as  a  glaze 
and  flux  in  the  manufacture  of  pottery. 

Sanidin. — Is  a  transparent  and  glassy  form  of  orthoclase, 
frequently  in  crystals  imbedded  in  lava. 

Adularia.—\s  a  white,  clear  orthoclase,  often  with  pearly 
opalescence. 

Albite,  Soda  Feldspar. 

Triclinic. — Usually  in  crystalline  masses  with  more  or 
less  lamellar  structure. 

In  composition  a  silicate  of  aluminum  and  sodium  ;  color 
generally  white  or  gray,  often  of  shades  of  blue,  red,  or 
green  ;  subtranslucent.  Is  not  acted  upon  by  acids ;  fuses 
with  difficulty  and  colors  flame  yellow. 

Albite  is  a  constituent  of  many  crystalline  rocks,  such  as 
diorite,  granite,  and  gneiss.  The  finest  crystalline  specimens 
occur  in  granite  veins.  Albite  frequently  shows  fine  striae 
on  cleavage  surfaces  due  to  intersection  of  faces  of  crystal- 
line laminae. 


88  DESCRIPTIVE  MINERALOGY. 


Microcline. 

This  species  is  in  composition  nearly  the  same  as  ortho- 
clase,  but  more  generally  contains  sodium.  It  is,  however,, 
triclinic,  though  the  cleavage  angle  varies  but  slightly  from 
a  right  angle. 

There  are  many  other  varieties  of  feldspar,  the  more  im- 
portant of  which  are  Anorthite,  Labradorite,  Andesite,  and 
Oligoclase.  The  first  named  is  a  calcium  feldspar,  and  the 
others  are  calcium  and  sodium  feldspars.  Anorthite  and 
Labradorite  are  sometimes  called  basic  feldspars  because 
they  contain  less  than  60  per  cent  of  silica ;  the  others  are 
termed  acid  feldspars.  Plagioclase  is  a  general  term  often 
used  to  include  all  the  triclinic  feldspars  except  microcline. 
The  feldspar  species  is  one  of  the  most  important  rock-mak- 
ing minerals. 

FELSPATHOID    GROUP. 

This  group  includes  several  silicates  of  aluminum  and  an 
alkali  metal,  and  in  this  respect  is  closely  related  to  the  feld- 
spars. The  group,  however,  have  different  crystalline  forms 
and  physical  properties,  and  in  the  arrangement  of  the  sili- 
cates already  referred  to  they  do  not  fall  in  the  same  class. 
as  the  feldspars.  The  more  important  species  of  the  fel- 
spathoid  group  are  given  below. 


Leucite,  Amphigene. 

Isometric. — Leucite  generally  occurs  in  crystals,  grains,  or 
granular  masses.  The  larger  crystals  often  show  inclusions 
of  foreign  matter  symmetrically  arranged. 

Leucite  is  a  silicate  of  aluminum  and  potassium,  the  lat- 
ter being  sometimes  replaced  in  small  quantity  by  sodium. 
Color  usually  dull  white  to  dark  gray  ;  streak  white.  H.  = 
5.5  to  6.  G.  =  2.4  to  2.5.  Brittle  with  conchoidal  fracture.. 
B.B.  infusible,  blue  color  with  cobalt  solution  by  ignition. 

Generally  found  in  recent  eruptive  rocks. 


ft^ir 

SILICATES.  89- 


Nephelite,  Nepheline. 

Hexagonal. — Occurs  in  white  columnar  crystals,  six-  or 
twelve-sided,  also  in  granular  masses  and  compact. 

Nephelite  is  a  silicate  of  potassium  and  sodium ;  its  color 
is  white  or  yellowish,  massive  varieties  dark  green,  bluish 
gray,  brown  or  red  ;  luster  vitreous  to  greasy.  H.  =  5.5  to  6. 
G.  =  2.55  to  2.65.  Brittle,  with  semi-conchoidal  fracture. 
B.B.  fuses  to  a  colorless  glass;  gelatinizes  with  acids. 

Nepljelite  occurs  in  both  recent  and  ancient  lavas,  also 
in  certain  plutonic  rocks. 

Analcite,  Analcine. 

Isometric. — Occurs  in  trapezohedra,  also  massive  and 
granular  ;  cleavage  cubical  but  imperfect. 

Analcite  is  a  hydrous  silicate  of  aluminum  and  sodium. 
Color  is  white,  sometimes  shaded  gray,  green,  yellow,  or 
red  ;  luster  vitreous.  H.  =  5  to  5.5.  G.  =  2.2.  Brittle,  with 
semi-conchoidal  fracture.  Gives  water  in  closed  tube. 
B.B.  fuses  without  difficulty  to  a  colorless  glass.  Gelatinizes 
with  hydrochloric  acid. 

Analcite  is  of  frequent  occurrence  in  cavities  and  seams 
in  basic  volcanic  rocks,  also  in  granite  and  gneiss. 

Of  the  species  here  included  in  the  felspathoid  group, 
leucite  and  nephelite  are  richer  in  alkali  than  the  feldspars, 
and  analcite  is  a  hydrous  silicate. 

Topaz. 

Orthorhombic. — Crystals  commonly  prismatic,  generally 
differently  modified  at  the  two  extremities,  faces  usually 
striated  vertically ;  also  massive  in  columnar  aggregates, 
coarse  or  fine  granular.  Perfect  cleavage  parallel  to  base. 

Topaz  is  a  silicate  of  aluminum  with  part  of  the  oxygen 
replaced  by  fluorine;  also  frequently  contains  hydroxyl. 
Its  color  varies  from  yellow,  through  gray  and  white  to 
shades  of  green,  blue,  or  red  ;  luster  vitreous  ;  streak  white  ; 


pO  DESCRIPTIVE   MINERALOGY. 

brittle.  H.  =  8.  G.  =  3.4103.6.  B.B.  infusible  ;  not  affected 
by  acids,  except  partially  by  H2SO4.  Distinguished  by  its 
hardness,  infusibility,  brilliant  and  easy  basic  cleavage. 

Topaz  most  generally  occurs  in  the  acidic  igneous  rocks, 
as  granite  and  rhyolite ;  also  in  metamorphic  schists.  It  is 
frequently  accompanied  by  fluorite,  tourmaline,  beryl,  and 
apatite.  The  transparent  and  colorless  varieties  are  used 
as  gems,  the  pink  crystals  being  most  valuable. 


Andalusite. 

Orthorhombic. — Crystals  generally  nearly  square  prisms, 
massive  and  indistinctly  columnar,  occasionally  radiated  and 
granular. 

Andalusite  is  a  silicate  of  aluminum  ;  some  of  the  alumi- 
num is  often  replaced  by  iron.  Color  white,  pearl-gray, 
pink  to  brownish  red  and  olive-green;  luster  vitreous; 
streak  uncolored;  brittle.  H.  =  7.5.  G.  =  3.  i  to  3.2.  B.B. 
infusible  ;  not  affected  by  acids.  Heated  with  cobalt  solu- 
tion gives  a  blue  color. 

Occurs  only  as  imbedded  crystals,  most  commonly  in 
schists. 

Kaolinite. 

Kaolinite  is  a  hydrous  silicate  of  aluminum  resulting 
mainly  from  the  decomposition  of  the  feldspars.  In  the 
course  of  time  rocks  containing  these  minerals,  such  as 
granite,  gneiss,  etc.,  are  disintegrated  by  aqueous  and 
atmospheric  agencies,  the  disintegration  being  due  to  the 
decomposition  of  the  feldspars. 

The  feldspars  in  passing  to  kaolinite  lose  their  alkaline 
and  lime  bases  and  part  of  their  silica  and  take  up  water. 
It  is  thought  that  the  carbon  dioxide  of  the  atmosphere  and 
other  organic  acids  are  the  essential  agents  in  removing  the 
bases  from  the  minerals.  With  the  change  in  the  feldspar, 
the  rock  crumbles,  and  both  the  kaolinite  and  the  associated 
constituents  are  eroded  and  carried  away  by  the  running 
waters  and  eventually  deposited. 


SILICATES.  91 

Kaolinite  is  ordinarily  called  kaolin.  When  pure  it  has 
a  soapy  feel,  white  color,  and  when  touched  to  the  tongue 
adheres  strongly.  When  breathed  upon  it  gives  the  well- 
known  clay  odor,  it  is  infusible,  not  acted  upon  by  acids 
under  ordinary  conditions,  and  yields  water  when  heated  in 
a  closed  tube. 

Common  clays  contain  more  or  less  kaolinite  mingled 
with  eroded  material  from  the  parent  rock  and  from  the 
rocks  over  which  the  depositing  waters  have  passed.  The 
minerals  most  frequently  mingled  with  the  kaolinite  are 
finely  divided  quartz,  feldspar,  and  mica. 

Common  clays  usually  contain  some  of  the  compounds  of 
iron,  and  if  these  are  of  such  nature  as  not  to  withstand  heat, 
the  clay  will  generally  burn  red,  due  to  the  transformation 
of  the  iron  compound  into  the  red  oxide.  The  ordinary 
alterable  iron  compounds  in  clay  are  the  limonite,  carbon- 
ate, or  perhaps  iron,  combined  with  some  organic  acid.  If 
the  iron  be  in  some  of  the  silicated  forms,  the  clay  does  not 
change  color  by  heat.  The  well-known  cream-colored 
Milwaukee  bricks  are  made  of  such  clay. 

The  use  of  clay  in  brick-making  is  well  known.  If  of 
good  clay,  brick  is  one  of  the  best  building-stones  to  resist 
heat.  Porcelain  is  made  of  the  purest  kaolin,  stoneware  of 
the  less  pure  varieties.  Fire-bricks  are  generally  made  of  a 
fine  quality  of  clay,  though  they  are  sometimes  composed 
of  a  large  per  cent  of  silica. 

Tourmaline. 

Hexagonal. — Prism  the  prevailing  form,  with  three  (or 
some  multiple  of  three)  sides.  Sides  usually  striated  or 
channeled.  Ends  of  crystals  frequently  unlike.  Also 
occurs  massive. 

Tourmaline  is  a  complex  silicate,  essentially  of  aluminum 
and  boron,  but  with  several  other  bases,  the  proportions  of 
which  are  believed  to  give  the  many  different  varieties. 

The  common  forms  are  usually  brown  or  some  shade  of 
black,  but  there  are  various  shades  of  red,  yellow,  and 


92  DESCRIPTIVE   MINERALOGY. 

green.  Generally  translucent  to  opaque.  H.  =  7.5.  It  is 
brittle,  fractured  surface  uneven.  Tourmaline  when  in 
crystals  is  distinguished  by  the  number  of  faces  being  some 
multiple  of  three.  Its  hardness  is  usually  sufficient  to  dis- 
tinguish the  dark  varieties  from  resembling  minerals. 

Rubellite  is  the  red  tourmaline. 

Indicolite  is  the  blue  tourmaline. 

Tourmaline  is  also  found  in  white,  blue,  and  green  colors. 

This  mineral  usually  occurs  penetrating  crystalline  rocks; 
it  is  not  an  essential  constituent.  The  fine  specimens  are 
highly  prized  as  gems. 

Specimens  that  rival  any  in  the  world  in  beauty  have 
been  found  in  Maine,  at  Paris  and  Hebron.  Fairly  fine 
specimens  have  been  found  in  many  other  States  of  the 
Union.  Ceylon  and  Brazil  have  also  given  celebrated 
crystals. 

Talc. 

Talc  is  a  hydrous  silicate  of  magnesium  and  nearly 
always  contains  a  little  iron.  Generally  occurs  in  foliated 
masses  with  a  pearly  luster,  readily  peeling  off  in  layers  ; 
masses  also  compact  and  of  fine  scales,  occasionally  granular 
and  less  often  fibrous.  Talc  is  usually  of  a  greenish- white 
color,  but  varies  to  other  shades  of  green  and  to  nearly  pure 
white.  In  the  laminated  variety  H.  =  i  to  1.5.  The  scales 
are  flexible  but  not  elastic.  Yields  water  with  difficulty 
when  heated  in  closed  tube.  Infusible  and  not  acted  upon 
by  acids.  All  varieties  have  a  greasy  feel. 

There  is  a  number  of  varieties  of  this  mineral,  of  which 
the  more  important  will  be  mentioned. 

Talc. — This  term  is  commonly  limited  to  the  more  dis- 
tinctly foliated  varieties. 

Steatite,  Soapstone. — Fairly  compact  or  finely  granular  in 
texture,  usually  greenish  gray  or  gray. 

French  Chalk. — The  white  laminated  variety,  used  for 
marking  on  cloth. 

Indurated  Talc. — An  impure  variety  of  a  somewhat  shaly 
texture,  with  hardness  of  3  to  4. 


SILICA  TES.  93 

Talc  occurs  in  many  of  the  States  and  in  Canada.  Penn- 
sylvania furnishes  the  greater  quantity  of  the  steatite, 
though  it  is  also  mined  in  Virginia,  North  Carolina,  and 
South  Carolina.  It  is  trimmed  into  slabs  for  various  uses — 
as  bath-tubs,  laundry -tubs,,  frames  to  hot-air  registers,  etc. 
In  the  powdered  form  it  is  largely  employed  as  a  filler  in 
mineral  paints  and  in  fire-retarding  paints.  Fibrous  talc  is 
extensively  mined  at  Gouverneur,  N.  Y.,  and  is  largely  used 
to  give  weight  and  filling  in  the  manufacture  of  paper. 
This  form  passes  under  the  name  of  mineral  pulp.  The 
powdered  form  is  also  used  as  a  lubricant  for  machinery  and 
for  diminishing  machinery  friction  generally.  Boot-powder 
is  composed  of  it. 

Serpentine. 

This  mineral,  like  talc,  is  also  a  hydrous  silicate  of 
magnesium,  but  contains  more  water  and  less  silica  than 
talc.  It  generally  occurs  massive  and  compact  and  finely 
fibrous.  Color  is  usually  some  shade  of  green,  more  often 
green  tinged  with  yellow,  though  sometimes  nearly  white. 
Luster  faintly  resinous  to  oily.  H.  =  2.5  to  4;  often  has 
greasy  feel,  but  less  so  than  talc.  Yields  water  readily 
when  heated  in  closed  tube,  and  changes  color  to  brown. 

Precious  Serpentine. — When  the  color  is  a  bright  tint  of 
yellow-green  and  the  mineral  translucent.  When  the 
mineral  is  opaque  and  the  color  dull  it  is  common  serpentine. 

Chrysotile. — This  is  the  finely  fibrous  variety  and  is  largely 
used  under  the  name  of  asbestus.  This  is  the  mineral  that 
is,  in  this  country,  generally  woven  into  fire-proof  roofing, 
clothes,  etc.  It  is  obtained  in  New  York,  but  much  more 
abundantly  in  Canada,  being  called  asbestus. 

Verd  Antique,  Ophiolite. — This  name  is  applied  to  a 
mineral  composed  of  a  mixture  of  serpentine  and  lime- 
stone. When  polished  it  gives  a  marble,  mottled,  and  often 
of  much  beauty.  Serpentine  itself  gives  a  marble,  but 
generally  not  so  variegated  as  when  calcite  is  present. 
Pennsylvania  furnishes  a  serpentine  which  is  used  as  a 
building-stone. 


94  DESCRIPTIVE   MINERALOGY, 

Chlorite. 

Chlorite  is  a  general  term  applied  to  a  group  of  minerals 
which  are  hydrous  silicates  of  magnesium  and  aluminum, 
and  in  which  iron  and  other  metals  are  usually  present  in 
small  quantity ;  less  silica  is  present  than  in  serpentine. 
The  term  chlorite  is  also  applied  to  the  more  important 
varieties  of  this  group,  which  are  of  extensive  occurrence, 
but  whose  compositions  are  not  well  determined  and  whose 
forms  are  not  distinctly  defined.  The  distinctly  crystallized 
species  are  not  of  great  importance.  When  the  word  is 
used  in  the  limited  sense  it  refers  to  the  dark  green  varieties 
which  occur  foliated  and  massive  and  also  in  fine  granular, 
almost  compact  forms  and  finely  fibrous.  H.  =  i  to  2. 
Streak  is  whitish  or  slightly  greenish,  yields  water  in  closed 
tube.  Color  due  to  the  large  per  cent  of  iron  present. 

MINERAL   COAL. 

This  important  substance  is  essentially  composed  of  car- 
bon, hydrogen,  oxygen,  a  little  nitrogen,  and  sulphur,  to- 
gether with  some  earthy  matter  which  gives  the  ash.  There 
may  also  be  a  little  moisture  present  and  sometimes  oc- 
cluded hydrocarbons,  but  these  are  accidents  in  the  coal. 
Coal  occurs  massive  and  uncrystallized,  is  from  brown  to 
black  in  color.  H.  =  1.5  to  2.5. 

Perfect  coal  when  pure  may  be  divided  into  two  general 
classes,  Anthracite  and  Bituminous,  depending  upon  the 
per  cent  of  volatile  ingredients  present. 

Anthracite. — This  coal  has  a  high  luster,  between  vitre- 
ous and  metallic,  color  glistening-black,  often  iridescent. 
H.  =:  2  to  2.5.  G.  —  about  1.6.  Often  gives  conchoidal  frac- 
ture ;  it  burns  with  a  pale  blue  flame.  In  this  coal  go  to  95 
per  cent  of  the  combustible  matter  is  fixed  carbon.  It  con- 
tains from  5  to  12  per  cent  of  earthy  matter,  which  is  left  as 
ash  in  burning.  The  volatile  matter  in  the  coal  ranges  from 
three  to  seven  per  cent.  It  is  sometimes  called  stone-coal  or 
glance. 


MINERAL    COAL.  9£ 

Bituminous  Coal. — This  coal  has  a  dull  or  slightly  resin- 
ous luster.  H.  =  1.5  to  2.  G.  =  about  1.3.  It  burns  with  a 
smoky  yellow  flame. 

In  this  coal  the  combustible  matter  contains  from  45  to 
85  per  cent  of  fixed  carbon,  from  15  to  55  per  cent  of  volatile 
matter;  there  is  present  from  i  to  8  per  cent  of  earthy  mat- 
ter. When  the  combustible  matter  contains  from  80  to  85, 
per  cent  of  fixed  carbon  and  15  to  20  per  cent  of  volatile 
matter  it  is  called  semi-bituminous.  When  the  volatile  mat- 
ter rises  to  30  or  40  per  cent  it  is  full  bituminous,  and  when 
beyond  this  per  cent  it  is  highly  bituminous. 

Common  bituminous  coals  are  generally  divided  into 
two  kind,  caking  and  non-caking.  Caking  coal  softens 
and  becomes  pasty  in  the  fire,  so  that  pieces  in  contact  ad- 
here, forming  a  solid  mass.  Non-caking  coal  burns  freely 
without  softening.  These  varieties  cannot  be  distinguished 
by  external  characters,  nor  has  the  chemical  difference  be- 
tween them  been  determined. 

Cannel  Coal. — A  highly  bituminous  variety,  of  compact 
texture,  with  little  luster,  and  conchoidal  fracture.  It  burns 
brightly  with  much  flame.  It  is  very  valuable  for  making 
gas  as  well  as  for  open-grate  burning. 

Brown  Coal. — An  imperfectly  formed  coal,  in  which  the 
conversion  of  the  vegetable  matter  into  coal  has  not  beea 
completed.  It  contains  from  15  to  35  per  cent  of  oxygen. 
It  is  of  a  brownish-black  or  black  color,  streak  brown. 
When  the  woody  structure  is  still  clearly  visible  it  is  called 
lignite. 

Jet. — This  is  a  very  black,  compact  variety  of  brown  coal. 
It  takes  a  high  polish  and  is  used  for  cheap  ornaments. 

In  addition  to  these  varieties  a  native  coke  has  been  found 
in  Virginia,  probably  resulting  from  the  action  of  eruptive 
rocks  on  bituminous  coal.  It  resembles  common  coke,  but 
is  more  compact. 

All  the  varieties  of  coal  may  contain  greater  or  less  pro- 
portions of  mineral  impurities,  giving  other  divisions  de- 
pending upon  the  degree  of  impurity.  If  the  ash  does  not 
amount  to  more  than  8  or  10  per  cent  in  anthracite,  the  coal 


9  DESCRIPTIVE   MINERALOGY. 

may  be  considered  as  pure.  The  pure  anthracite  gives 
more  ash  than  the  pure  bituminous,  which  was  to  be  ex- 
pected, as  the  former  results  from  a  condensation  of  the 
latter.  The  mineral  matter  making  up  the  ash  of  pure  coal 
comes  from  the  plants  out  of  which  the  coal  was  formed. 
It  consists  mainly  of  silica,  alumina,  oxide  of  iron,  lime  in 
small  quantity,  and  a  little  potash  and  magnesia. 

The  origin  of  coal  and  the  location  of  the  beds  are  given 
in  Geology. 


TABLES  FOR  USE  IN  THE  DETERMINATION 
OF  MINERALS. 

THESE  tables  have  been  constructed  with  the  view  of 
facilitating  the  determination  of  the  minerals  of  the  text. 
The  order  of  arrangement  and  the  directions  for  use  of 
the  tables  are  intended  .to  develop  and  improve  the  powers 
of  comparison  and  observation,  as  well  as  to  bring  about  a 
correct  determination  of  the  mineral  species. 

The  minerals  are  classified  under  three  general  sub- 
divisions, A,  B,  and  C. 

A  includes  all  the  minerals  with  a  distinctly  metallic 
luster. 

B  includes  all  minerals  that  have  not  a  distinctly  metallic 
luster,  but  have  a  colored  streak. 

C  includes  all  minerals  with  an  unmetallic  luster  and  an 
uncolored  streak. 

In  the  first  subdivision  (A)  the  minerals  are  again  clas- 
sified according  to  color ;  in  the  second  (B)  according  to 
streak;  and  in  the  third  (C)  according  to  hardness;  and  in 
each  of  these  smaller  classes  the  minerals  are  arranged  in 
the  order  of  their  hardness. 

The  tables  consist  of  two  principal  parts ;  in  the  first 
are  given  the  external  characteristics  of  the  minerals ;  in 
the  second  are  described  the  effects  of  acids  and  of  heat. 
The  former  should  always  be  examined  first.  Some  speci- 
mens can  be  determined  from  external  characteristics  alone, 


TABLES  fOR   DETERMINATION   OF  MINERALS.  97 

and  many  others  can  be  limited  to  a  small  number  of  species. 
The  method  of  procedure  in  the  determination  of  minerals 
should  be  as  follows: 

Take  up  the  specimen  and  note  its  luster,  whether 
metallic,  semimetallic,  or  unmetallic  ;  if  metallic,  note  its 
color ;  if  semimetallic  or  unmetallic,  determine  its  streak. 
Finally,  determine  the  hardness  of  the  specimen.  Now  try 
to  place  it  as  rapidly  as  possible  in  the  table  :  in  A  by  its 
color  first,  then  by  its  hardness;  in  B  by  its  streak  first, 
then  by  its  hardness  ;  in  C  by  its  hardness  alone.  When 
the  specimen  under  consideration  is  thus  approximately 
determined,  see  if  the  other  characters  given  in  its  descrip- 
tion correspond  to  what  is  observed  in  the  specimen.  This 
is  all  that  can  be  accomplished  by  the  use  of  the  first  part 
of  the  tables ;  for  further  verification  the  directions  in  the 
second  part  of  the  tables  must  be  followed  and  the  effects 
of  acids  and  heat  observed.  For  a  proper  use  of  the  tables 
the  student  must  be  familiar  with  the  contents  of  Chapter 
II,  which  precedes,  and  must;  also  have  instruction  and  as- 
sistance in  the  use  of  the  appliances  of  the  mineralogicai 
laboratory. 


98 


A.— MINERALS   WITH 

EXTERNAL    CHARACTERISTICS. 


No. 

Species. 

Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

I.— BED  OB  BROWN. 


Copper 

Copper  red 

Copper  red 

H.=2.7 

Malleable 

Proustite 

Scarlet  ver- 
milion 

Scarlet,  ver- 
milion, 

H.=2.5 

Brittle 

sometimes 

orange 
yellow 

Bornite 

(Erubescite) 

Brownish 
red 

Dark  gray- 
ish black 

H.=3.o 
Brittle 

Cuprite 

Red  to 
brown 

Brownish 
red 

H.  =3.5104 
Brittle 

Rutile 

Red  to 
brownish 
red 

Gray  to 
yellowish 
brown 

H.=6to6.5 
Brittle 

Cassiterite 

Brown  to 
reddish 
brown 

Gray  to 
light 
brown 

H.=6  to  7 
Brittle 

Crystals  isometric;  occurs 
usually  massive  and  in 
plates  or  strings  penetrat- 
ing the  gangue;  clings  to 
a  file.  G.>8 

Generally  found  with  other 
ores  of  silver,  especially 
with  pyrargyrite,  cerargy- 
rite,  and  native  silver 


Color   decidedly  more    red 
than  that  of  chalcopyrite 


Sometimes  in  octahedrons, 
but  often  massive,  gran- 
ular,and  earthy;  frequent- 
ly contains  iron  oxide^ 
G.  =  5.8  to  6.1 

Distinguished  from  tin  ore 
by  not  giving  tin  with 
soda  on  charcoal 

Practically  the  only  ore  ofi 
tin.  G.=6.8  to  7.1* 


II.— YELLOW. 


7 

Gold 

Golden  yel- 

Yellow 

H.  =  2.5 

Crystals    isometric,   occurs 

low 

Malleable 

usually  in  grains,  strings, 

or   plates  in  a  gangue  of 

quartz,    the    latter    being 

often  discolored   by  iron- 

Clings  to  a  file.     G.>i$ 

8 

Chalcopyrite 

Bronze  yel- 

Greenish 

H.=4-2 

Often  tarnished  and  irides- 

low 

black 

Brittle 

cent,  sometimes  green  on 

surface  ;    purer    varieties 

have  deeper  color 

METALLIC    LUSTER. 


99 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

Cu 


Ag3AsS3 


Cu3FeS3 


Cu20 


TiO, 


SnOj 


Acted  upon  by  HNOs,  hy- 
drogen escaping  ;  addi- 
tion of  ammonia  to  diluted 
solution  gives  blue  color 


Acted  upon  by  HNO3  with 
separation  of  sulphur 


After  careful  roasting  par- 
tiallyactedupon  by  HNO3, 
and  addition  of  ammonia 
to  diluted  solution  gives 
blue  color 

Acted  upon  by  HNOs  and 
diluted  solution  gives  blue 
color  with  ammonia 


No  action 


Not  perceptibly  acted  upon 
by  acids 


On  charcoal  fuses  easily 
and  gives  odors  of  sul- 
phur and  arsenic  oxide; 
white  sublimate  in  open 
tube.  With  soda  and  re- 
ducing flame, bead  of  silver 

Fuses  readily  to  a  black 
magnetic  globule 


Fuses  easily  in  forceps  and 
colors  flame  green;  yields 
bead  of  copper  on  char- 
coal 


B.  B.  infusible  alone 


B.  B.  alone  infusible;  with 
soda  on  charcoal  reduced 
to  metallic  tin  and  gives 
white  coating  ;  requires 
long  blowing 


Au 


CuFeS, 


No  action 


After  careful  roasting  par- 
tiallyacted  uponby  HNO3, 
and  addition  of  ammonia 
to  diluted  solution  gives 
blue  color 


Fuses     without      difficulty, 
but  no  action  with  fluxes 


Carefully  roasted  and' 
mixed  with  soda  and 
heated  on  charcoal,  gives 
a  globule  of  copper 


100 


A.— MINERALS    WITH 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

II. -YELLOW. 


9     Pyrrhotite 


10 


Pyrite 


Bronze  yel- 

Grayish 

H.  =3.5104 

low 

black 

Brittle 

Brass  yel- 

Brownish 

H.=6 

low 

black 

Brittle 

III.-WHITE. 


12 


Silver 

Silver  white 

Silver  white 

H.=2.5 

Malleable 

Arsenopyrite 

(Mispickel) 

Tin-white 
to  gray- 
ish 

Grayish 
black 

H.  =  5-5 
Brittle 

Usually  slightly  magnetic. 
Composition  varies,  but 
conforms  to  the  general 
formula  FenSn-|  i 

Isometric;  sometimes  mas- 
sive, but  generally  in 
crystals  disseminated 
through  rocks.  Sides  of 
cubes  often  striated  at 
right  angles  to  each  other. 
Harder  than  chalcopyrite 


Isometric;  occurs  in  strings 
or  plates  disseminated 
through  the  gangue; 
clings  to  a  file;  generally 
tarnished  on  exposed  sur- 
face. G.  =  10.5 

Hard,  strikes  fire  with  steej 
and  emits  odor  of  garlic. 
G.=6 


IV.-GRAY. 


13 

Graphite 

Iron  gray 

Black,  shin- 
ing 

H.  =  i 

Friable 

Feels  greasy,  soils  paper; 
micaceous  or  scaly,  rarely 
compact.  Often  dissemi- 
nated through  rock  in  fine 
scales.  G.  =  2.25 

14 

Molybdenite 

Lead  gray, 
inclining 
to  black 

Bluishgray, 
shining 

H.  =  i.5 

Friable 

Feels  greasy;  occurs  thin, 
tabular,  or  scaly;  soils 
paper.  G.>4 

15 

Stibnite 

Lead  gray 

Dark  gray- 
ish black 

H.=2.5 
Brittle 

Burns  in  flame  of  candle; 
slightly  sectile.  Princi- 
pal ore 

METALLIC    LUSTER.        '.  ,,•/»*, 


I  £       10 1 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

Fe7S6 


FeS2 


Acted  upon  by  HC1  with 
liberation  of  hydrogen 
sulphide 


Roasted  first;  slightly  acted 
upon  by  HC1;  addition  of 
K4FeCy6  gives  blue  pre- 
cipitate 


B.  B.  fuses  easily  to  a  black 
magnetic  globule 


B.  B.  sulphurous  odor  and 
fuses  to  magnetic  globule 


12 


Ag 


FeAsS 


Acted  upon  by  HNO3;  ad- 
dition of  HC1  gives  a 
white  curdy  precipitate, 
soluble  in  ammonia.  Cop- 
per plate  placed  in  nitric 
solution  becomes  coated 
with  silver 


On  charcoal  alliaceous 
odor,  giving  white  coating 
on  coal;  leaves  magnetic 
globule.  In  closed  tube 
gives  a  black  sublimate  of 
arsenic;  sometimes  red 
and  yellow  sublimates 


No  action 


MoSa  Acted  upon  by  HNO8,  giv 

ing  a  grayish   residue  of 
molybdic  oxide 


Sb-Sa  When  pure,  acted  upon  by 

HC1;  HNO3  causes  a  sep- 
aration of  sulphur  and 
antimony  pentoxide 


Mixed  with  niterand  heated 
in  closed  tube,  deflagrates 


In  forceps  colors  flame 
green;  finely  powdered, 
gives  sulphurous  odor  in 
open  tube 

Fuses  easily  and  gives 
white  fumes  and  volatile 
white  coating  on  charcoal 


102 


A.— MINERALS   WITH 


EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

IV.-GBAY. 


16 


18 


21 


Argentite 

Blackish 
lead  gray 

Blackish 
lead  gray 

H.=2.5 
Malleable 

Galenite 

Bluish  gray 

Dark  gray 

H.=2.7 
Friable 

Chalcocite 

Blackish 
lead  gray 

Dark  lead 
gray  to 
black 

H.  =2.  5103 
Brittle 

Tetrahedrite 

Dark  gray 
to  black 

Dark  gray 
to  black, 

H.=3to  4 
Brittle 

and  inclin- 

ing to  red 

Tennantite 

Blackish 
lead  gray 
to  black 

Dark  gray 
to  black, 
sometimes 

H.=3to  4 
Brittle 

reddish 

Hematite 

Specular 
iron  ore 

Between 
iron  black 
and    dark 

Cherry  red, 
brownish 
red 

H.=6.5 
'Brittle 

steel  gray 

Can  be  cut  like  lead  when 
massive;  is  usually  finely 
disseminated  through  the 
gangue.  Most  common 
ore  of  silver.  G.  -  7.3 


Is  chief  ore  of  lead.  Often 
has  characteristic  cubical 
cleavage  which  is  easily 
obtained.  Also  occurs  in 
granular  masses;  very  of- 
ten contains  some  silver 
sulphide.  The  ore  be- 
comes more  micaceous  as 
the  silver  sulphide  in- 
creases. G.  >  7  « 

Somewhat  resembles  argen- 
tite,  but  is  not  sectile 


Often  a  valuable  ore  of  sil- 
ver, the  copper  being  in 
part  replaced  by  silver 


Closely  related  to  tetrahe- 
drite,  the  antimony  being 
wholly  or  partly  replaced 
by  arsenic 

Hexagonal;  occurs  com- 
pact, scaly,  fibrous;  some- 
times slightly  magnetic* 
G.=4-9  t°  5-3 


V.— BLACK. 


22 

Graphite 

Iron  black 

Black,  shiny 

H.  =  i 
Friable 

Other    characteristics     the 
same  as  the  gray  variety, 
13  above 

METALLIC 


LUSTER. 


103 


No. 

Composition. 

Action 

of  Acids. 

Effects  of 

Heating. 

r6 


18 


Ag,S 


PbS 


Cu,S 


Cu8S7Sba 


Cu8S7As2 


Fe,03 


Acted  upon  by  HNO3,  with 
separation  of  sulphur;  ad- 
dition of  HC1  gives  a 
white  curdy  precipitate, 
soluble  in  ammonia.  Cop- 
per plate  placed  in  nitric 
solution  becomes  coated 
with  silver 

Acted  upon  by  HNO3,  with 
separation  of  sulphur  and 
formation  of  some  lead 
sulphate;  addition  of  am- 
monium sulphide  gives 
black  precipitate 


Acted  upon  by  hot  HNO3, 
with  separation  of  sul- 
phur; solution  coats  knife 
blade  with  copper 

Acted  upon  by  HNO3,  and 
addition  of  ammonia  to 
dilute  solution  gives  blue 
color.  (Copper  test) 


Acted  upon  by  HC1;  addi- 
tion of  K4FeCy«  to  dilute 
solution  gives  blue  pre- 
cipitate 


Sulphurous  odor  in  open 
tube;  fuses  easily  on  char- 
coal and  gives  globule  of 
silver 


On  charcoal  decrepitates; 
sulphurous  odor;  gives 
yellow  coating  on  coal 
and  yields  globule  of  lead 


On  charcoal  powder  gives 
sulphurous  odor  and 
leaves  globule  of  copper 


Fuses  easily  on  charcoal, 
giving  sulphurous  odor 
and  white  sublimate;  a 
globule  of  copper  after 
long  heating  with  soda 


Infusible,  but  easily  be- 
comes magnetic  on  char- 
coal 


No  action 


Same  as  13  above 


104 


A.— MINERALS    WITH 

EXTERNAL    CHARACTERISTICS. 


No. 

Species. 

Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

V.—  BLACK. 

23 

Argentite 

Grayish 

black 

Gray  black 

H.=2t02.5 

Malleable 

Same  as  16  above 

24 

Pyrolusite 

Iron  black 
to  bluish 
black 

Black,  blu- 
ish black, 
sometimes 
shining 

H.=2t02.5 

Brittle 

The  common  ore  of  manga- 
nese ;  occurs  compact  to 
unconsolidated.  G.—  4.8 

25 

Pyrargyrite 

Black,  red 
by  trans- 
mitted 
light 

Purplish 
red 

H.=2to  2.5 
Brittle 

Occurs  with  other  ores  of 
silver.  G.  =  5.8 

26 

Stephanite 

Black  to 
iron  black 

Black  to 
iron  black 

H.=2  to  2.  5 
Brittle 

Brittle  with  uneven  frac- 
ture. G.  >6 

27 

Chalcocite 

Grayish 
black 

Grayish 
black 

H.  =  2.  5  to  3 
Brittle 

Often  tarnished  blue  or 
green.  G.  =  5-5  to  5.8 

28 

Melaconite 

Black  to 
gray 

i 

Black 

H.  =  3  to  4 
Brittle  to 
earthy 

Black  masses  and  concre- 
tions along  with  other 
ores  of  copper.  G.  =  5.8 
to  6.2 

29 

Chromite 

Black,  iron 
black, 
brown 
black 

Yellow, 
gray  or 
dark 
brown 

H.  =  5  to  5.  5 
Brittle 

Generally  magnetic,  some- 
times strongly  so.  G.= 
4-3 

30 

Magnetite 

Iron  black 

Black 

H.  =  5.5 
Brittle 

[sometric  ;  granular  or  com- 
pact ;  black  streak  and 
magnetic  property  usually 
distinguish  it.  G.  >5 

V 

Franklinite 

Iron  black 

Brownish 
black 

H.  =  5.5  to 
6.5 
Brittle 

Isometric.  Resembles  mag- 
netite, but  generally  has 
more  earthy  black  color, 
usually  feebly  magnetic 

32 

Hematite 

Between 
iron  black 
and  dark 
steel  gray 

Cherry  red, 
brownish 
red 

H.=6.5 
Brittle 

Hexagonal.  Occurs  com- 
pact, scaly,  fibrous,  some- 
times slightly  magnetic. 
G.  =4.9  to  5.3 

METALLIC   LUSTER. 


ios 


No. 

Composition. 

Action  of 

Acids. 

Effects  of 

Heating. 

23 
24 


26 


27 


29 


Ag2S 
MnOa 

Ag3SbS< 


Ag,SbS< 


Cu2S 


CuO 


FeCr204 


Fe,04 


Oxides  of 
iron,  zinc, 
and  manga- 
nese 

Fe303 


Same  as  16  above 


Acted    upon   by   HC1    with 
evolution  of  chlorine 


Same  as  16  above 


Amethystine      bead      with 
borax  in  oxidizing  flame 


Acted  upon  by  HNOa,  with   On    charcoal    fuses    easily 
separation  of  sulphur  and      with       spurting,       giving 
antimony  oxide.      Copper 
plate  in  nitric  solution  be- 


comes coated  with  silver 


Acted  upon  by  HNO8,  with 
separation  of  sulphur. 
Copper  plate  in  nitric  so- 
lution becomes  coated 
with  silver 

Same  as  18  above 


Acted  upon  by  HNOj,  and 
gives  copper  test  with  am- 
monia as  in  4  and  8 


Not  acted  upon 


Acted  upon  by  HC1.     Gives 
iron  test,  same  as  21  above 


Acted  upon  by  HC1  with 
occasional  evolution  of 
chlorine.  Gives  iron  test 
as  in  21 

Gives  iron  test  with 
K4FeCy6,  same  as  21 


white  coating  of  antimony 
oxide.  With  soda  in  re- 
ducing flame  gives  silver; 
red  sublimate  in  open 
tube,  white  in  closed 


On  charcoal  gives  sulphur- 
ous odor;  fumes  and  coat- 
ing of  antimony.  With 
soda  a  globule  of  silver 


Same  as  18  above 


Gives  copper  with  soda  on 
charcoal 


Gives  emerald  green  color 
to  bead  of  borax  and  salt 
of  phosphorus 


B.  B.  infusible 


Amethyst  bead  with  borax, 
bluish  green  bead  with 
soda 


Same  as  21 


io6 


A.— MINERALS   WITH 

EXTERNAL    CHARACTERISTICS. 


No. 

Species. 

Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

V.-BLACK, 

33 

Rutile 

Black 

Gray  to 

light 
brown 

H.  =6  to  6.5 
Brittle 

Distinguished  from  tin  ore 
by  not  yielding  tin  with 
soda  on  charcoal.  G.= 

4-2 

34 

Cassiterite 

Black 

Gray  to 
light 
brown 

H=6to7 
Brittle 

Principal  ore  of  tin.  G.= 
6.8 

B.— MINERALS  WITHOUT 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

I.-STREAK  GRAY,  BLACK,   OB  GREEN. 

35  •  Graphite 

L.  Semi- 

Black  or 

H.  =  i 

Luster    sometimes    dull    or 

metallic 

dark  gray 

Friable 

earthy  black,   other  char- 

C. Iron 

acters  same  as  13 

black  to 

dark  gray 

36 

Coal 

L.  Resinous 

Grayish 

H.  =  2.5 

Usually  shows  lamination; 

(Bitumin- 

to vitre- 

black 

Friable 

the  cannel  coal  is  compact 

ous) 

ous;  some- 

Brownish 

Brittle 

with    large   conchoidal 

times 

black 

fractures.       Decomposing 

silky 

pyrite  in  coal  produces  a 

C.   Black 

gray  or  yellowish  powder 

with  inky  taste.     G.  =1.03 

37 

Melaconite 

L.  Unmetal- 

Black 

H.=2.5 

A  black  powder  or  massive 

Tenorite 

lic 

Friable 

and  compact;  often  stained 

C.   Black 

greenish;      soils      fingers 

when  massive  or   pulver- 

ulent.    G.>5.5 

38 

Coal 

L.  Semi- 

Black 

H.=2.75 

Hard,    with     high     luster; 

(Anthracite) 

metallic; 

Very 

breaking  with   small  con- 

vitreous 

brittle 

choidal  fracture.     G.  =  i.6 

C.  Black 

39 

Amphibole 

L.  Vitreous 

Dark  gray 

H.  =  5-6 

Monoclinic;    crystals    long 

(Horn- 

C. Black  to 

to  green- 

Tough 

and  slender,  cleavage  ob- 

blende 

greenish 

ish  gray 

Brittle 

lique,   124°;    massive   spe- 

black 

cimens  have  black  color, 

common  luster,  are  often 

made  up  of  bladed  crystals 

intersecting    in    all   direc- 

tions.    G.=3.3 

METALLIC   LUSTER. 


107 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

33  TiOa  No  action 


34 


SnOa 


Not  perceptibly  acted  upon 
by  acids 


Infusible  alone 


B.  B.  alone  infusible;  with 
soda  on  charcoal  yields 
metallic  tin  and  gives 
white  coating  ;  requires 
long  blowing 


METALLIC  LUSTER;  STREAK  COLORED. 


No. 

Composition. 

Action  of  Acids. 

Effects  of  Heating. 

35 


37 


39 


Carbon    with 
some  hydro- 
gen and 
oxygen 


CuO 


Carbon 


Magnesium, 
calcium, 
iron  and 
aluminum 
silicate 


No  action 


No  action 


Acted  upon  by  HNO3;  ad- 
dition of  ammonia  to  dil- 
uted solution  gives  blue 
color 


Thoroughly  mixed  with 
niter  deflagrates  in  closed 
tube 


In  forceps  burns  with  yel- 
low flame.  Thoroughly 
mixed  with  niter,  defla- 
grates in  closed  tube 


Gives  copper  with  soda  on 
charcoal.  Moistened  with 
HC1,  colors  B.  B.  pipe 
flame  azure  blue 


Burns  without  flame;  gives 
no  odor.  Thoroughly 
mixed  with  niter,  defla- 
grates in  closed  tube 

Anhydrous  ,  fusible  with 
intumescence  in  forceps 
or  on  charcoal 


io8 


B._ MINERALS   WITHOUT  METALLIC 

EXTERNAL    CHARACTERISTICS. 


No.l 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

•_    Remarks. 

I.— STREAK  GRAY,  BLACK,  OR  GREEN. 


40 


42 


Pyroxene 
(Augite) 

L.  Vitreous 
C.  Gravish 
black, 
greenish 
black 

Dark  gray, 
greenish 
gray 

H.=6 
Tough 
Brittle 

Franklinite 

L.  Semi- 
metallic  to 

Black 

H.=6.25 
Brittle 

dull  vitre- 

ous 

C.   Black 

Magnetite 

L.   Semi- 
metallic, 

Black 

H.=6.25 
Brittle 

vitreous 

C.   Black 

Monoclinic;  crystals  short 
and  stout,  cleavage 
nearly  rectangular;  gran- 
ular varieties  are  called 
coccolite;  massive  speci- 
mens are  often  composed 
of  stout  crystals  with 
ends  projecting  on  the 
surface.  G.=3.4 

Isometric;  occurs  in  octa- 
hedrons; usually  slightly 
magnetic  due  to  Fe3O4. 
Often  occurs  with  red 
zincite 

Isometric;  in  small  octahe- 
drons; usually  in  granular 
masses;  magnetic,  heavy. 
G.>5 


II.— STREAK  BROWX. 


43 

Lignite 

L.  Dull, 
generally  ; 
if  shining, 
resinous 
C.  Brown, 

Brown, 
verging 
on  black 

H.=2.5 
Friable 

Sometimes  laminated;  gen-     ' 
erally      showing      woody 
structure;     often    earthy; 
peat     contains      rootlets; 
air-dried      contains     con- 

black 

siderable  water.     G.  =  i.2 

44 

Cuprite 

(impure) 

L.  Common 
C.  Brown 

Brown 

H.=4 

Brittle 

Impure    with    clay;     often 
stained  green  on  surface. 
G.>4 

45 

Sphalerite 

L.  Resinous 
Adaman- 

Yellow to 
brown 

H.=4 
Brittle 

Isometric;      cleavage     dis- 
tinct.    G.=4 

tine 

Vitreous 

C.  Black, 

brown 

LUSTER;  STREAK  COLORED. 


IOQ 


No. 

Composition. 

Action 

of  Acids. 

Effects  of 

Heating. 

40 


42 


Magnesium, 
calcium, 
iron,  and 
aluminium 
silicate 


Oxide  of  Zn, 
Fe,  and  Mn 


Fe804 


Same  as  for  31 


Acted  upon  by  HC1;  after 
dilution  addition  of 
K4FeCy6  gives  blue  pre- 
cipitate 


Anhydrous;  fusible  with 
intumescence  in  forceps 
or  on  charcoal 


Becomes  magnetic;  when 
fused  with  soda  and  some 
niter  on  platinum  foil  the 
manganese  present  usu- 
ally colors  the  mass  green 

Borax  bead  is  bottle-green 
in  R.  F.,  in  O.  F.  it  is  yel- 
low while  hot,  colorless 
when  cold 


43  . 


44 


45 


Carbon, 
hydrogen, 
oxygen 


Cu,0 


ZnS 


Acted  upon  by  HNO8;  after 
dilution,  addition  of  am- 
monia colors  solution 
blue 

Effervesces  in  hot  HC1  with 
evolution  of  H2S 


Burns  with  yellow  flame  in 
forceps;  gives  off  empy- 
reumatic  odors.  Mixed 
with  niter  deflagrates  in 
closed  tube 


Fuses  easily  in  forceps  and 
colors  flame  green.  Yields 
bead  of  copper  on  char- 
coal 

Pulverized  and  heated  on 
charcoal  gives  sulphur- 
ous odor  ;  slight  zinc 
fumes;  coating  near  assay 
which  is  yellow  while  hot, 
white  on  cooling.  In  open 
tube,  very  little  (if  any) 
sublimate  of  sulphur; 
slight  odor  of  SO2  and  an 
acid  reaction 


110 


B.— MINERALS   WITHOUT 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

II.— STREAK  BROWN. 


46 


47 


Limonite 

L.  Vitreous, 

Yellowish 

H.  =  5-5 

resinous, 

brown 

Brittle 

silky, 

pearly 

C.  Brown 

Amphibole 

L.  Common 

Yellowish 

H.  =  5.5 

(Basaltic 

C.  Black 

brown, 

Brittle 

hornblende) 

issr 

brown 

Cassiterite 

L.  Adaman- 

Gray to 

H.=6.5 

tine 

light 

Brittle 

C.  Brown 

brown 

to  black 

Rutile 

L.  Adaman- 

Light 

H.=6to6.5 

tine 

brown 

Brittle 

C.  Reddish 

brown  to 

red,  black 

49 


III.— STREAK  RED. 


Usually  earthy  or  botry- 
oidal,  with  a  fibrous  tex- 
ture. G.  >4 


Monoclinic  ;  cleavage  of 
crystals  oblique  124°; 
massive  specimens  often 
are  made  up  of  bladed 
crystals  intersecting  in  all 
directions.  G.  =  3.3 

When  of  composition  given 
sometimes  called  basaltic 


Principal  tin  ore.     G.=6.8 


Very     like      tin     ore,     dis- 
tinguished as  stated  in  33 


Hematite 

(Red  chalk) 

L.  Common 
C.  Dark  red 

Brownish 
red 

H.=2 

Friable 

Massive,  pulverulent,  or 
compact;  earthy;  rather 
light 

Cinnabar 

L.  Adaman- 
tine 
C.  Cochi- 
neal red 

Scarlet 

H.=2  102.5 
Friable 

Massive  granular,  glisten- 
ing in  specks;  earthy 
when  impure;  volatile. 
G.  from  3  to  8,  >  8  when 

pure 

METALLIC    LUSTER;    STREAK   COLORED. 


i  u 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

46     2FeaO3,3HaO 


47 


49 


Magnesium, 
calcium, 
iron,  and 
aluminum 
silicate 


SnOa 


TiO5 


Acted  upon  by  HC1;  after 
dilution  addition  of 
K4FeCy6  gives  blue  pre- 
cipitate 


Not  perceptibly  acted  upon 
by  acids 


Not  acted  upon 


Gives  off  much  water  easily 
in  closed  tube.  Borax 
bead  is  bottle  green  in  R. 
F. ;  in  O.  F.  yellow  while 
hot,  colorless  cold.  On 
charcoal  becomes  black 
and  magnetic 

Anhydrous.  In  forceps  or 
on  charcoal  fuses  with  in- 
tumescence 


B.  B.  alone  infusible;  with- 
soda  on  charcoal  yields 
metallic  tin  and  gives 
white  coating;  requires, 
long  blowing 

Infusible  alone 


Fea03 


HgS 


Slightly  acted  upon  by 
HC1;  addition  of  K4FeCy6 
to  dilute  solution  gives 
blue  precipitate 


Not  acted  upon  by  either 
nitric  or  hydrochloric 
acid:  attacked  by  aqua 
regia  with  separation  of 
sulphur 


On  charcoal  becomes  mag- 
netic if  not  too  impure. 
Often  gives  off  water  in 
closed  tube,  due  to  clay 
present 

Heated  in  closed  tube  with 
sodium  carbonate  gives 
sublimate  of  i^ercury  in 
small  globules;  alone 
gives  a  black  sublimate, 
wholly  volatile  when  pure. 
In  open  tube  gives  sul- 
phurous odor 


112 


B.— MINERALS   WITHOUT 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

III.— STREAK  RED. 


Proustite 


53 


'54 


S5 


Pyrargyrite 


Cuprite 


Hematite 


L.  Adaman- 
tine to  dull 
C.  Scarlet 
vermilion 

Scarlet  ver- 
milion 

H.=2  tO  2.  5 

Brittle 

Generally  found  with  other 
ores  of  silver.     See  2,  G. 
=  5-6 

L.  Adaman- 
tine todul] 
C.  Black  to 
deep  red 

Purplish 
red 

H.=a.S 
Brittle 

Occurs  with  other  ores  of 
silver,  G.=5.8 

L.  Adaman- 
tine, semi- 
metallic, 
common 
C.  Carmine 
red,  red- 
dish lead 

Brownish 
red 

H.=4 

Brittle 

Cleavage  distinct;  often 
impure  from  clay;  .copper 
ores  are  often  stained 
green  on  the  surface.  G. 
=  .5.8  to  6.1 

gray 

L.Common, 
semi-me- 
tallic 
C.  Dark 
red.   Part- 
ly steel 
gray 

Brownish 
red 

H.  =5  (vari- 
able) 
Brittle 

Massive,  granular,  fibrous, 
lenticular,  pulverulent, 
rarely  botryoidal.  G.>4 

IV.-YELLOW. 


56 

Limonite 

L.  Common 

Yellow 

H.  =  i 

Usually  earthy,  containing 

(Yellow 

C.  Yellow 

Friable 

much  clay;  very  light 

ocher) 

57 

Sulphur 

L.  Resin- 

Straw yel- 

H.=2 

G.-2 

ous,  ada- 

low   ' 

Brittle 

mantine 

Friable 

C.  Sulphur 

yellow, 

grayish 

yellow 

METALLIC   LUSTER;   STREAK   COLORED.        113 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

52         AgaAsSs 


53 


54 


55 


AgsSbSs 


CuaO 


Fe,0s 


Acted  upon  by  HNO3,  with 
separation  of  sulphur 


Acted  upon  by  HNO3,  with 
separation  of  sulphur. 
Copper  plate  in  nitric  so- 
lution coated  with  silver 


Acted  upon  by  HNOs;  ad- 
dition of  ammonia  to  di 
lute    solution    gives    blue 
color 


Acted  upon  by  HC1;  addi- 
tion of  K4FeCy«  to  dilute 
solution  gives  blue  color 


On  charcoal  fuses  easily 
and  gives  odors  of  sul- 
phurous and  arsenic 
oxides.  White  sublimate 
in  open  tube.  With  soda 
and  reducing  flame  bead 
of  silver 

On  charcoal  fuses  easily, 
with  spurting,  giving 
white  coating  of  antimony 
oxide.  With  soda  in  re- 
ducing flame  gives  silver; 
red  sublimate  in  closed 
tube,  white  in  open 

B.  B.  colors  flame  green 
and  fuses  readily,  yield- 
ing metallic  copper  on 
charcoal 


Anhydrous;  becomes  mag- 
netic on  charcoal 


57 


Acted  upon  by  HNOs;  ad- 
dition of  K4FeCy6  to  di- 
lute solution  gives  blue 
precipitate 


Becomes  magnetic,  if  not 
too  impure.  Gives  much 
water  easily 

Burns  with  blue  flame  and 
sulphurous  odor 


114 


B.— MINERALS   WITHOUT 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

IV.-YEL.L.OW. 


58 

Cinnabar 
(impure) 

L.  Common 
C.  Yellow- 
ish red, 
cochineal 

Yellow 

H.=2.25 

Friable 

Massive  granular,  glisten- 
ing in  specks;  earthy,, 
containing  clay 

red 

59 

Sphalerite 

L.  Resin- 
ous, ada- 
mantine 
C.  Gray, 
brown 

Light  yel- 
low to 
brown 

H.=4 
Brittle 

Isometric  ;  cleavage  of 
crystals  eminent;  massive 
Missouri  blende  is  glis- 
tening on  a  fresh  surface; 
often  contains  iron. 

G.=4 

60 

Siderite 

L.  Vitreous 
to  pearly 
C.  Yellow, 
yellowish 

Pale  yellow, 
brown 
when 
weathered 

H.=4 
Brittle 

Rhombohedral;  crystals 
often  curved;  often  brown 
or  black  by  weathering. 
G.=4 

gray  to 
yellowish 

brown 

61 

Zincite 

L.  Adaman- 
tine 
C.  Red, 

Orange 
yellow, 
brownish 

H.=4 
Brittle 

Cleavage  distinct,  often  in 
laminated  aggregations; 
occurs  with  Franklinite. 

orange, 
brown 

yellow 

G.>4 

62 

Limonite 

L.Common, 
silky 
C.  Brown 

Brownish 
yellow, 
ocher 
yellow 

H.  =  5.5 
Brittle 

Usually  earthy  or  botry- 
oidal,  with  a  fibrous  tex- 
ture; bog  ore  is  sometimes 
loose,  porous  and  earthy. 
G.>4 

63 

Amphibole 
(Basaltic 
horn- 
blende) 

L.  Common 
C.  Brown- 
ish black 

Grayish 
yellow, 
ocher 
yellow 

H.  =  5.5 
Brittle 

Monoclinic;  cleavage 
oblique,  124°;  crystals 
usually  long  and  slender, 
often  acicular  or  bladed; 

massive  specimens  are 
nearly  black  and  some- 
times made  up  of  bladed 
crystals  intersecting  in 
all  directions.  When  of 

composition  given  some- 
times called  basaltic  horn- 

blende 

METALLIC   LUSTER;   STREAK   COLORED.        115 


No. 

Composition. 

Action 

of  Acids. 

Effects  of 

Heating. 

59 


60 


61 


62 


HgS 


ZnS 


FeCO3 


ZnO 


2FeaO3,3H2O 


Magnesium, 
calcium, 
iron,  and 
aluminum 
silicate 


Not  acted  upon  by  either 
nitric  or  hydrochloric 
acid.  Attacked  by  aqua 
regia  with  separation  of 
sulphur 


Acted  upon  by  HC1,  pro- 
d  u  c  i  n  g  effervescence, 
evolving  H2S 


When  powdered,  hot  HC1 
acts  upon  it,  producing 
effervescence;  addition  of 
K4FeCye  to  dilute  solution 
gives  blue  precipitate 


Acted  upon  by  acids 


Acted  upon  by  acids;  addi- 
tion of  K4FeCye  to  dilute 
solution  gives  blue  pre- 
cipitate 


Mixed  with  soda  and  heat- 
ed in  closed  tube  gives 
small  globules  of  mercury 
on  side  of  tube;  alone 
gives  a  black  sublimate. 
In  open  tube  gives  sul- 
phurous odor 

On  charcoal  sulphurous 
odor,  zinc  fumes;  coating 
(near  assay)  which  is  yel- 
low while  hot,  becoming 
white  on  cooling 


Blackens  and  becomes 
magnetic  in  reducing 
flame 


On  charcoal,  zinc  fumes; 
coating  (near  assay)  which 
is  yellow  while  hot,  be- 
coming white  on  cooling 


Becomes  magnetic  in  re- 
ducing flame;  gives  much 
water  in  closed  tube 


Anhydrous;  on  charcoal  or 
in  forceps  fuses  with  in- 
tumescence 


B.— MINERALS   WITHOUT  METALLIC 

EXTERNAL    CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

Remarks. 

V.— STREAK  GREEN. 


64 

Chlorite 

L.  Common, 

Grayish 

H.  =  2.s 

Schistose  in  structure;  often 

pearly 

green 

Friable 

earthy  by  weathering;  its 

C.  Dark 

fracture      is      micaceous, 

green 

compact,  or  earthy;  cleav- 

age eminent,  folia  flexible 

but  not  elastic 

65 

Serpentine 

L.  Resinous 

Grayish 

H.=3 

Amorphous;  massive;  when 

(impure) 

(weak) 

green 

(variable) 

impure  it  is  earthy,  when 

C.  Green, 

Friable 

pure  its  fracture  is  splin- 

F 

yellow, 

Brittle 

tery;  unctuous  feel;  when 

and  some- 

breathed upon  smells  bit- 

times 

ter;  often  mixed  with  cal- 

white; 

cite 

rarely 

dark 

^>-~ 

66 

^Chrysocolla 

L.  Vitreous 

Bluish 

H.=2.4  to  3 

Amorphous;      often      reni- 

to  earthy, 

green  to 

Friable 

form;  compact  in  texture 

resinous 

white 

Brittle 

and  fracture;  accompanies 

C.  Green 

when  pure 

other   ores   of  copper,  es- 

pecially malachite;  seldom 

pure 

67 

Malachite 

L.  Vitreous, 

Emerald 

H.=3.5 

Often  reniform  ;    compact, 

pearly, 

green, 

Brittle 

fibrous,  or  earthy.     G.=4 

silky 

paler  than 

C.  Emerald 

color 

green 

68 

Crocidolite 

L.  Silky  to 

Same  as 

H.=4 

Opaque 

dull 

color 

Fibers 

C.  Laven- 

slightly 

der  blue 

elastic 

or  leek 

green 

69 

Pyroxene 

L.  Common 

Grayish 

H.=5.S 

Monoclinic;    crystals  short 

(Common 

C.  Blackish 

green 

Brittle 

and    stout,    cleavage    dis- 

augite) 

green 

tinct,   nearly  rectangular; 

usually  massive  granular 

or  composed  of  stout  crys- 

tals  with  ends  projecting 

on  surface 

LUSTER;  STREAK  COLORED. 


117 


No. 

Composition. 

Action 

of  Acids. 

Effects  of 

Heating. 

64 


66 


68 


69 


Hydrous, 
magnesium 
iron,  and 
aluminum 
silicate 


Hydrous, 
magnesium 
silicate 


Hydrous, 
copper 
silicate 


Hydrous, 
copper 
carbonate 


Iron  and  so- 
dium sili- 
cate; a  form 
of  asbestos 


Magnesium, 
calcium, 
iron,  and 
aluminum 
silicate 


HaSO4  and  HC1  act  upon  it 
with  a  separation  of  silica 


Acted  upon  slightly  by 
HNO3  ;  addition  of  am- 
monia to  dilute  solution 
gives  blue  color.  In  HC1 
decomposes  with  separa- 
tion of  SiO2  without  gelat- 
inization 

Acted     upon     by     HNO3 
diluted,    addition   of    am 
monia       colors      solution 
blue.       Effervesces     with 
acids 

Not  acted  upon  by  acids 


Gives    off    water     readily; 
does  not  change  color 


Gives  off  much  water  very 
readily;  color  changes  to 
brown 


Gives  off  much  water  read- 


B.  B.  decrepitates  and 
blackens  ;  colors  flame 
green;  gives  off  much 
water  easily 


In  closed  tube  gives  a  little 
water.  B.  B.  fuses  to  a 
black  magnetic  glass,  col- 
oring flame  yellow 


Fusible  with  intumescence.- 


u8 


B.— MINERALS  WITHOUT   METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Luster  and 
Color. 

Streak. 

Hardness  and 
Tenacity. 

.Remarks. 

V.-STREAK  GREEN. 


70 


Amphibole 

L.  Common 

Grayish 

(Common 

C.  Blackish 

green 

horn- 

green 

blende) 

.  =  5.5 

Brittle 


Monoclinic  ;  crystals  long 
and  slender,  often  acicu- 
lar;  cleavage  oblique,  124°; 
granular  or  lamellar;  usu- 
ally a  mass  of  bladed  crys- 
tals 


TI.-STREAK  BLUE. 


ri 

Chrysocolla 

L.  Vitreous, 

Greenish 

H.=2.4to  3 

Amorphous  ;      often    reni- 

resinous 

blue,  smalt 

Friable 

form;  compact  in  texture 

C.  Blue 

blue 

Brittle 

and    fracture  ,     accompa- 

nies other  ores  of  copper, 

especially  malachite 

'2 

Azurite 

L.  Vitreous 

Smalt  blue 

H.=3-75 

Often  in  incrustations;  com- 

C.  Lazuli 

Brittle 

pact,    fibrous,    or    earthy. 

blue 

G.=4 

73 

Lapis  Lazuli 

L.  Vitreous 

Smalt  blue 

H.=5.5 

Often     contains    scales    of 

C.  Lazuli 

Brittle 

mica  ;     usually     compact. 

blue 

G.  =  2.5 

C.— MINERALS   WITHOUT   METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

I.-VERY   SOFT. 


74 

Calcite 

White 

Common 

H.—  0.5  to  i 

Usually  a  soft,  white,  por- 

(Rock milk) 

Pulverulent 

ous,    earthy   mass  ;    very 

light 

LUSTER;    STREAK  COLORED. 


119 


No. 

Composition. 

Action  of 

Ac 

ids. 

Effects  of 

Heating. 

70 


Magnesium, 
calcium, 
iron,  and 
aluminum 
silicate 


Fusible  with  intumescence 


72 


73 


Hydrous, 
copper  sili- 
cate 


Hydrous, 
copper  car- 
bonate 


Sodium,  alu- 
minum 
silicate, with 
sodium  sul- 
phide and 
sulphate 


Acted  upon  by  HNO3;  addi- 
tion of  ammonia  to  dilute 
solution  gives  blue  color. 
In  HC1  decomposes  with 
separation  of  SiO2,  with- 
out gelatinization 

Acted  upon  by  HNOsI  solu- 
tion diluted,  gives  blue 
color  on  addition  of  am- 
monia. Effervesces  with 
acids 

Slowly  acted  upon  by  HC1, 
giving  odor  of  HaS 


Gives  off  much  water  easily 


B.  B.  decrepitates  and 
blackens  ;  colors  flame 
green.  Gives  off  much 
water  easily 


Fusible;  loses  its  color 


LUSTER;   STREAK   WHITE   OR   LIGHT    GRAY. 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

74 


CaCO, 


Acted  upon  with  efferves- 
cence by  HNO3  and  HC1; 
addition  of  H2SO4  to  di- 
luted solution  gives  white 
precipitate 


Infusible;  assay  after  igni- 
tion reacts  alkaline 


120 


C.— MINERALS    WITHOUT   METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

I.-VEBY  SOFT. 


75 

Kaolinite 

White 

Pearly 

H.  =  i 

Usually  a  soft,  white,   im- 

Friable 

palpable  earthy  mass,  with 

unctuous  feel   and   clayey 

taste  and  odor.     Ordinary 

clay    consists    largely    of 

kaolinite 

76 

Talc 

White, 

Eminently 

H.  =  i 

Usually  in  foliated  or  com- 

green 

pearly 

Friable 

pact  masses,  with  an  unc- 

Sectile 

tuous  feel;    folia   flexible; 

cleavage  eminent 

77 

Calcite 

White,  gray 

Common 

H.  =  i 

Usually   a   compact,    white 

(Chalk) 

to  brown 

Friable 

mass,  composed  of  shells. 

of  foraminifers 

78 

Cerargyrite 

Gray  to 

Resinous  to 

H.  =  i  to  1.5 

Very  valuable  ore  of  silver; 

(Horn  sil- 

brown, 

dull 

Highly 

easy    of   treatment;    com- 

ver) 

green,  and 

sectile 

mon    in    South    America, 

blue 

when  pure 

Mexico,     and      southern 

United  States.      Plate    of 

iron    rubbed    with    it   be- 

comes silvered.     G.  =  5-5 

79 

Niter 

White 

Vitreous 

H.  =  i.75 

Taste    saline    and   cooling  ; 

Friable 

occurs  in  incrustations  or 

Brittle 

crystallized  in  right  rhom- 

bic prisms 

80" 

Gypsum 

White, 

Vitreous, 

H.=2 

Occurs     compact,     fibrous, 

gray,  yel- 

silky, 

Friable  to 

and     foliated,    sometimes 

low,  red, 

pearly 

brittle 

fine      granular;    cleavage 

and 

eminent;  folia  flexible. 

brown 

G.  =  2.3 

81 

Sulphur 

Yellow, 

Adaman- 

H.=2 

Compact,  in    crusts  or  pul- 

grav» 

tine,  resi- 

Brittle to 

verulent.     G.=2 

brown 

nous 

friable 

82 

Mica 

Gray, 

Pearly 

H.=2.5 

Usually  in  foliated  or  mica- 

(Muscovite) 

white, 

Friable 

ceous      masses      or      thin 

pale  yel- 

sheets; cleavage  eminent; 

low  or 

folia  tough  and  elastic 

brown 

LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

75 


76 


77 


79 


80 


Si 


Hydrous, alu- 
minum sili- 
cate 


Hydrous, 
magnesium 
silicate 


CaCO, 


AgCl 


KN09 


CaSO4,2H2O 


Hydrous,  po- 
tassium, 
aluminum 
silicate 


No  action 


No  action 


Gives  off  much  water  read- 
ily 


Exfoliates  before  blowpipe. 
Yields  very  little  water  (if 
any)  with  difficulty 


Acted  upon  by  HNO3  and   Infusible;  assay  after  igni- 
HC1    with    effervescence  ;!     tion  reacts  alkaline 
H2SO4  added  to  dilute  so-l 
lution  gives  white  precipi- 
tate 

Not  acted  upon  by  HNOs  or  Fuses  in  flame  of  candle ;  on 
HC1,  but  soluble  in  am-  charcoal,  metallic  bead  of 
monia  silver 


Fuses  in  closed  tube;  bits 
of  charcoal  dropped  in 
cause  deflagration 

Fuses;  leaves  assay  which 
is  alkaline.  Gives  off  wa- 
ter easily 


Dissolves  in  hot  HC1  or 
HNO3;  after  dilution  ad- 
dition of  barium  chloride 
gives  white  precipitate 


Burns    with   a   blue    flame 
sulphurous  odor 


Yields  little  water  in  closed 
tube 


122 


Q— MINERALS   WITHOUT    METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

I.-VERY  SOFT. 


•83 

Mica 

Black 

Pearly 

H.=2.5 

Usually  in   foliated  or  mi- 

(Biotite) 

Brittle  to 

caceous    masses    or    thin 

friable 

sheets;  cleavage  eminent; 

folia  tough  and  elastic 

84 

Chlorite 

Green; 

Pearly 

H.=a.5 

Schistose  in  structure;  of  ten 

rarelv 

Friable 

earthy  by  weathering;  its 

bluish 

fracture       is     micaceous, 

red 

compact,  or  earthy;  cleav- 

age  eminent;    folia  flexi- 

ble but  not  elastic 

«5 

Halite 

White, 

Vitreous  to 

H.  =  2.0 

Isometric,    in   cubes;    mas- 

gray, red 

resinous 

Brittle  to 

sive,  compact,  or  granular; 

friable 

taste  saline 

86 

Cryolite 

White  to 

Vitreous  to 

H.=2.5 

Massive;  fracture  uneven. 

brown 

greasy 

Brittle 

G.=3 

87 

Anglesite 

White, 

Adaman- 

H.=2.7 to  3 

G.=6.i  to  6.4 

gray  to 

tine  to 

Brittle 

yellowish 

vitreous 

88 

Carnallite 

Red 

Vitreous  to 

H.  =  2.7 

Soluble     in     water,    bitter 

greasy 

Sectile 

taste,  deliquescent 

II.—  SOFT. 

89 

Calcite 

All  colors; 

Vitreous 

H.r=3 

Crystals  and  cleavage 

white, 

Brittle 

rhombohedral  ;    usually 

gray,  and 

compact,    granular,  or 

reddish 

fibrous  ;    sometimes  tufa- 

common 

ceous  ;    impure    varieties 

often  contain  clay  and  sil- 

ica.    G.  =  2.7 

90 

Anhydrite 

Gray, 

Vitreous, 

H.=3 

Usually    compact  ;    harder 

white,  and 

resinous, 

Brittle 

and  heavier  than  gypsum; 

bluish 

pearly 

fracture    often    splintery. 

gray 

G.=3.o 

123 
LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Composition. 

Action  of  Acids. 

Effects  of 

Heating. 

Hydrous, 
potassium, 
magnesium 
iron,  alu- 
minum 
silicate 

Hydrous, 
magnesium, 
iron,  alu- 
minum 
silicate 


NaCl 


Fluoride  of 
sodium  and 
aluminum 

PbSO4 


Mixture  of 
potassium 
and  mag- 
nesium 
chlorides 


Soluble  in  H2O;  addition  of 
solution  of  silver  salt 
gives  white, curdy  precipi- 
tate of  silver  chloride. 


Yields  little  water  in  closed 
tube 


Gives  off  a  moderate  quan- 
tity of  water  rather  read- 
ily; does  not  change  color 


Fusible  ;   colors   flame    yel- 
low 


Fuses  easily  in  flame  of 
candle  ;  colors  flame  yel- 
low 

Fuses  easily;  metallic  lead 
on  charcoal 


Fuses  easily 


CaCOs 


CaS04 


Acted  upon  by  HC1  and 
HNOs,  effervesces.  Solu- 
tion diluted,  addition  of 
HaSO4  gives  white  precip- 
itate 


Dissolves  in  hot  HC1  and 
HNO3;  addition  (after  di- 
lution) of  barium  chloride 
gives  white  precipitate 


Infusible;  assay  after  igni- 
tion reacts  alkaline 


Fuses;  assay  after  ignition 
reacts  alkaline  ;  gives  off 
little  or  no  water 


124 


C.— MINERALS   WITHOUT    METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

II.-SOFT. 

9i 

Cerussite 

White  to 
gray 

Adaman- 
tine to 

H.  =  3  to  3.5 
Brittle 

Occurs  massive  and  stalac- 
titic.     G.=6.5 

vitreous 

92 

Witherite 

White 

Vitreous 
to  resi- 

3 to  3.5 
Brittle 

G.=4.3 

nous 

93 

Chrysocolla 

Verdigris 
green,  sky 
blue 

Shimmer- 
ing (vitre- 
ous, silky) 

H.=3-5 
Brittle 

Amorphous  ;  often  reni- 
form;  compact  in  texture 
and  fracture;  accompanies 
other  ores  of  copper,  es- 
pecially malachite 

94 

Aragonite 

White,gray, 
pale  yel- 
low 

Vitreous, 
silky 

H.=4 
Brittle 

Common  in  columnar  ag- 
gregations ;  harder  than 
calcite.  G.=2.9 

95 

Serpentine 

Yellow, 
green,  and 
sometimes 
white; 
rarely 
dark 

Resinous 
(weak) 

H.=4 

Brittle, 
friable 

Amorphous;  massive;  when 
pure  its  fracture  is  splin- 
tery, when  impure  it  is 
earthy  ;  unctuous  feel  ; 
when  breathed  upon 
smells  bitter;  often  mixed 

green 

with  calcite 

96 

Sphalerite 

Yellowish 

Adaman- 
tine 

H.=4 

Brittle 

Isometric,  cleavage  of  crys- 
tals eminent  ;  massive 

Missouri  blende  is  glisten- 
ing on  a  fresh  surface. 
G.=4 

97 

Fluorite 

White, 
grayish, 
light 
greenish 
and 
bluish, 

Vitreous 

H.=4 

Brittle 

Isometric  ;  cleavage  octa- 
hedral, distinct  ;  occurs 
crystallized,  also  massive, 
granular  ;  generally  1'ght 
colors.  G.=3 

common 

98 

Dolomite 

White  or 
grayish 

Vitreous, 
pearly 

H.=4 
Brittle 

Rhombohedral  ;  usually  a 
crystalline  mass  ;  often 
brown  by  weathering  ;  a 
little  harder  and  heavier 

than  calcite.  G.=2.g 

125- 


LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Con 

Q  position. 

Action  of  Acids. 

Effects  of 

Heating. 

91 


92 


'93 


'94 


95 


•96 


98 


PbCO5 


BaCO, 


Hydrous, 
copper 
silicate 


CaCO< 


Hydrous, 
magnesium 
silicate 


ZnS 


CaF, 


CaMg(C03), 


Readily    acted     upon 
HNO3,  effervesces 


by  Yields  lead  with  soda  on 
charcoal,  alone  if  heated 
carefully 


Acted  upon  by  HC1  with 
effervescence  and  dilute 
acid  solution  gives  white 
precipitate  with  H2SO4 

Acted  upon  by  HNO3;  ad- 
dition of  ammonia  colors 
solution  blue.  Decom- 
posed by  HC1  with  separa- 
tion of  white  silica,  with- 
out gelatinization 

Acted  upon  by  HC1  with 
effervescence  ;  after  dilu- 
tion, addition  of  sulphuric 
acid  gives  white  precipi- 
tate 


Effervesces     with      HC1 
strong  odor  of  HaS 


Dissolves  quietly  in  HC1 
solution  diluted,  netraliz- 
ed  with  ammonia  and  ox- 
alic  acid    added,  gives   a 
white  precipitate 


When  powdered, acted  upon 
by  HC1  with  efferves- 
cence; after  dilution, addi- 
tion of  H2SO4  gives  white 
precipitate 


Fuses  easily,  color  flame  to 
yellowish  green. 


Gives  off  much  water  easily 


Infusible;  assay  after  igni- 
tion reacts  alkaline 
Anhydrous 


Gives  off  much  water  very 
readily;  changes  color  to 
brown 


Pulverized,  heated  on  char- 
coal, sulphurous  odor; 
slight  zinc  fumes;  coating 
(near  assay)  yellow  while 
hot,  white  on  cooling 

Phosphoresces  and  decrep- 
itates; fuses;  assay  after 
ignition  reacts  alkaline 


Infusible  ;  assay  after  igni- 
tion reacts  alkaline 


126 


C— MINERALS  WITHOUT  METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

II.-SOFT. 


99  Siderite 


100 


101 


Smithsonite 


Calamine 


Yellow, 
yellowish 

Vitreous  to 
pearly 

H.=4 
Brittle 

gray, 
yellowish 
brown 

Gray,  green, 
blue, 
brown  to 

Vitreous, 
pearly  to 
dull 

H.  =4.5  to  5 
Brittle  to 
friable 

white 

Gray,  yel- 
low to 

Vitreous  to 
dull 

H.  =4.5  to  5 
Brittle 

brown 

Rhombohedral;  crystals  of- 
ten curved;  often  brown 
or  black  by  weathering. 


Found  in  veins,  but  more 
generally  in  deposits  of 
limestone;  usually  results 
from  alteration  of  ZnS. 


Stalactitic,  botryoidal,  fib- 
rous, also  massive  and 
granular.  G.=3.5 


III.-HARD. 


102 

Pyroxene 

Dark  green, 

Semi-metal- 

H.=4.75 

Monoclinic;      lamellar      or 

(Diallage) 

brown  or 

lic,  pearly 

Brittle 

tabular;    cleavage    nearly 

gray 

rectangular.     G.=3«4 

103 

Amphibole 

White  gray, 

Vitreous, 

H.=4-75 

Monoclinic;    crystals   long, 

(Tremolite) 

greenish 

silky 

Brittle 

slender  and   bladed,  often 

white 

fibrous      (asbestos);      fre- 

quently   in    crystals    dis- 

seminated through  a  mass 

of      dolomite;       cleavage 

oblique,  124°.     G.=3 

104 

Amphibole 

Green 

Vitreous, 

H.=4-75 

Monoclinic;    crystals    long 

(Actinolite) 

silky 

Brittle 

and     slender,     sometimes 

fibrous  (asbestos);  usually 

in  fibrous  crystals  dissemi- 

nated  through  a  mass  of 

talc  or  serpentine.     G.=3 

105 

Analcite 

White  to 

Vitreous 

H.  =4.5105.5 

Isometric;  trapezohedrons, 

pale  red 

Brittle 

rarely    massive.      G.  =  2.3 

to    2.4.     Transparent     to 

opaque 

127 


LUSTER;    STREAK  WHITE  OR  LIGHT  GRAY. 


No. 

Composition. 

Action 

of  Acids. 

Effects  of  Heating. 

100 


FeC03 


ZnCOs 


Hydrous, 
zinc  silicate 


When  powdered  acted  upon 
with  effervescence  by  hot 
HC1;  after  dilution  addi- 
tion of  K4FeCy6  gives  blue 
precipitate 

Acted  upon  by  HC1,  effer- 
vesces 


Gelatinizes  perfectly  in  HC1 


Blackens  and  becomes  mag- 
netic in  reducing  flame 


Coating  of  zinc  oxide  with 
soda  on  charcoal 


Yields  water  in  closed  tube 


102 

Calcium, 

Fusible  with  intumescence 

magnesium, 

iron,  silicate 

103 

Magnesium, 

Fusible  with  intumescence 

calcium, 

silicate 

104 

Calcium, 

Fusible  with  intumescence 

magnesium, 

and  iron 

silicate 

v 

, 

105 

Hydrous, 

Water  in  closed  tube;  fuses 

silicate  of 

easily  to  colorless  glass 

sodium  and 

aluminum 

-128 


Q— MINERALS  WITHOUT  METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

III.— HARD. 


106 

Apatite 

Usually 

Vitreous  to 

H.  =  5 

Hexagonal;    crystals    are 

green, 

somewhat 

Brittle 

hexagonal    prisms    with 

sometimes 

resinous 

pyramidal      terminations, 

brown, 

having   a   more    resinous 

etc. 

luster    than    beryl  ;    often 

massive.     G.=3.2 

107 

Willemite 

White  to 

Vitreous 

H.=5-5 

Usually   massive  ;   also    in 

gray,  yel- 

Brittle 

hexagonal  crystals. 

low,  green, 

G.=3.g  to  4.2 

brown 

108 

Enstatite 

Gray,  yel- 

Vitreous to 

H.=5.5 

Orthorhombic;  occurs  mas- 

low, green 

pearly 

Brittle 

sive,   fibrous,    and    lamel- 

to brown 

lar;  translucent  to  opaque. 

G.  =  3.i  to  3.3 

109 

Bronzite 

Gray,  yel- 

Vitreous to 

H.  =  5.5 

Enstatite  contains  little  or 

low,  green 

pearly 

Brittle 

no  iron,  bronzite  contains 

to  brown 

over  5  per  cent  of  iron 

no  Monazite 

Red  to  dark 

Adaman- 

H. =5  to  5.5 

Monoclinic;  generallyfound 

brown, 

tine  or 

Brittle 

as  rounded  grains  of  sand, 

reddish 

resinous 

sometimes  known  as  tho- 

or yellow- 

rium sand;  translucent 

ish  brown 

in 

Hypersthene 

Darkish 

Vitreous, 

H.=5to  6 

Orthorhombic  ;       massive, 

green  to 

resinous, 

Brittle 

tubular  and  lamellar. 

brown  and 

pearly, 

G.=3.4  to  3.5 

black 

almost 

metallic 

112 

Amphibole 

Black 

Vitreous 

H.=5-75 

Monoclinic  ;    crystals  long 

(Horn- 

Tough 

and  slender;  cleavage  ob- 

blende) 

lique,  124°;  granular;  mas- 

sive specimens  have  com- 

mon luster  and  often  con- 

sist of  a  mass  of  interlaced 

bladed    crystals.     G.=3-3 

I29 


LUSTER;    STREAK  WHITE  OR  LIGHT  GRAY. 


NO. 

Composition. 

Action 

of 

Acids. 

Effects  of  Heating. 

106  Calcium 

phosphate 


Zinc  silicate 


Magnesium, 
iron  silicate 


Magnesium, 
iron  silicate 


Phosphate  of 
cerium, 
lanthanum, 
and  didym- 
ium 

Iron  and 
magnesium 
silicate,  alu- 
minum 
sometimes 
present 

Magnesium, 
aluminum, 
calcium, 
iron  silicate 


Soluble  in  hot  HC1  or 
HNO3.  Solution  treated 
with  H2SO4  gives  precipi- 
tate of  calcium  sulphate. 
The  nitric  acid  solution 
added  to  excess  of  ammo 
nium  molybdate  produces 
immediately,  or  by  gentle 
warming,  a  bright  yellow 
precipitate,  which  shows 
the  presence  of  phosphor- 
ic acid 


Soluble    with    difficulty   in 
HC1 


Anhydrous.  Fuses  with 
difficulty  ;  coating  of  zinc 
oxide  with  soda  on  char- 
coal, yellow  while  hot, 
white  on  cooling 

Fusible  with  difficulty 


B.  B.  infusible 


B.  B.  on  charcoal  fusible 
with  difficulty  to  a  black 
magnetic  mass 


Fusible  with  intumescence 


130 


C.— MINERALS   WITHOUT   METALLIC 

EXTERNAL   CHARACTERISTICS. 


No 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

III.— HARD. 


113 

Pyroxene 

White  or 

Vitreous 

H.  =  5.75 

Monoclinic  ;  crystals   short 

(Malacolite) 

gray 

Brittle 

and  stout;  cleavage  near- 

ly rectangular  ;    granular 

varieties  are  called  cocco- 

lite  ;    massive     specimens 

often  composed  of  crystals 

with    ends  projecting    on 

surface.     G.  =3.4 

114 

Leucite 

White  to 

Vitreous  to 

H.  =5.5106 

Isometric;  trapezohedrons, 

gray 

resinous 

Brittle 

sometimes  massive,  trans- 

lucent to  opaque 

H5 

Nephelite 

White  to 

Vitreous  to 

H.  =  5.5106 

Hexagonal;  transparent  to. 

gray  or 

greasy 

Brittle 

opaque 

yellow 

Ii6 

Pyroxene 

Grayish 

Vitreous 

H.=6 

Monoclinic;    crystals    short 

(Augite) 

black, 

Tough, 

and  stout;  cleavage  nearly 

greenish 

brittle 

rectangular;  granular  va- 

black 

rieties  are  called  coccolite; 

massive     specimens     are 

often  composed  of  crystals 

with  their  ends  projecting 

on  the  surface.     G.=3.4 

*I7 

Orthoclase 

Reddish, 

Vitreous, 

H.=6 

Monoclinic  ;    two  cleavage 

gray, 

pearly  on 

Brittle 

planes    at    right    angles  ; 

white,  yel- 

cleavage 

cleavage      eminent,     seen 

low,  rarely 

surface 

when  broken  with  a  ham- 

green 

mer  ;    breaks    into  pieces 

resembling    rhombohe- 

drons.     G.  =2.6 

118 

Albite 

White 

Vitreous, 

H.=6 

Triclinic;  usually  a  mass  of 

pearly  on 

Brittle 

interlacing    bladed    crys- 

cleavage 

tals.      G.:=2.62 

surface 

119 

Turquois 

Bluish 

Somewhat 

H.=6 

Massive,  reniform,  without 

green 

waxy 

Brittle 

cleavage.     G.=2.y 

120 

Opal 

White,  yel- 

Resinous 

H.  =  5-5  to 

Amorphous  ;    generally    in 

lowish,  or 

6.5 

rounded    masses    with    a 

brownish, 

Brittle 

compact,  conchoidal   frac- 

common 

ture;  opalescent,  present- 

ing internal  reflections 

LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Composition. 

Action  of  Acids. 

Effects  of  Heating-. 

114 


116 


Magnesium, 
calcium  sil- 
icate 


118 


119 


120 


Silicate  of 
aluminum 
and  potas- 
sium 

Silicate  of 
aluminum 
and  potas- 
sium 

Magnesium, 
calcium, 
iron,  alu- 
minum sili- 
cate 


Potassium, 
aluminum 
silicate 


Sodium,  alu- 
minum sili- 
cate 


Hydrous, 
aluminum 
silicate 

SiO2 


Decomposed  by  HC1  with- 
out gelatinization 


Gelatinizes  with  acids 


No  action 


No  action  with  acids 


Soluble  in  HC1 


No  action  with  acids 


Fusible  with  difficulty,   in- 
tumescence 


B.  B.  infusible 


B.    B.    fuses    quietly   to   a 
colorless  glass 


Fusible  with  intumescence. 
Anhydrous 


Fuses  with  difficulty 


Fusible  with  difficulty,  col- 
oring flame  yellow 


Infusible;  becomes  brown. 
Gives  off  water 


Gives  off  water;  fuses  with 
effervescence  when  heated 
with  soda  on  charcoal 


132 


C.— MINERALS    WITHOUT    METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

III.-HAKD. 


Microline 


122 


Rutile 


White  to 
light 
cream  yel- 
low, also 
red,  green 

Vitreous, 
sometimes 
pearly 

H.=6to6.5 
Brittle 

Red  to 
brown 

Adaman- 
tine 

H.=6to6.5 
Brittle 

Same  in  composition  as 
orthoclase,  but  triclinic; 
translucent  to  transparent 


Tetragonal,  often  prismatic 
and  striated;  translucent 
to  opaque.  G.=4.2 


IV.— VERY  HARD. 


123 

Olivine 

Green,  yel- 

Vitreous 

H.-6.75 

Occurs    usually    in    grains, 

(Chrysolite) 

low 

Brittle 

or  granular  disseminated 

through    basalt    in    small 

glassy  crystals;  transpar- 

ent to  translucent. 

124 

Quartz 

White, 

Vitreous 

H.=7 

Hexagonal,     rhombohedral 

(Vitreous) 

gray,  light 

Brittle 

division;    crystals     trans- 

pink, and 

parent,       in        hexagonal 

amethyst 

prisms      with      pyramidal 

blue  are 

terminations;  no  cleavage 

common 

apparent;       occurs       also 

massive,    either    compact 

» 

or  granular 

125 

Quartz 

Brown, 

Somewhat 

H.=7 

Cryptocrystalline;   translu- 

(Chalce- 

yellow, 

waxy 

Tough 

cent;  mamillary,  nodular, 

donic) 

white,  and 

or  in  layers  lining  cavities; 

red  are 

compact,    breaking     with 

common 

conchoidal  fracture 

126 

Quartz 

Red,  brown, 

Common 

H.=7 

Cryptocrystalline;    opaque; 

(Jaspery) 

green,  and 

dull 

Tough 

usually  in  compact  masses, 

yellow  are 

, 

sometimes  banded 

common 

127 

Garnet 

Yellow, 

Vitreous  to 

H.=7 

In     separate    disseminated 

brown, 

resinous 

Brittle 

crystals      (dodecahedrons 

red,  and 

or  trapezohedrons)  or    in 

black  are 

granular    masses;     trans- 

common 

parent  to  opaque.       G.>3 

and    <5.        Pyrope    is    in 

small  granules 

133 
LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Con 

aposition. 

Action  of 

Acids. 

Effects  of 

Heating. 

121!  Potassium, 
aluminum 
silicate 


122 


TiOs 


No  action  with  acids 


Not  acted  upon 


Fuses  with  difficulty 


Infusible  alone 


123 


124 


125 


126 


127 


Magnesium, 
iron  silicate 


SiO2 


SiO5 


SiO2 


Calcium, 
magnesium, 
iron, 

aluminum 
silicate 


No  action  with  acids 


No  action  with  acids 


No  action  with  acids 


No  action  with  acids 


Infusible  (whitens). 


Fuses  with  effervescence 
with  soda  on  platinum 
wire  or  on  charcoal 


Fuses  with  effervescence 
with  soda  on  platinum 
wire  or  on  charcoal 


Fuses  with  effervescence 
with  soda  on  platinum 
wire  or  on  charcoal 


Dark  varieties  are  fusible, 
usually  leaving  a  mag- 
netic globule;  others  in- 
fusible 


134 


C— MINERALS   WITHOUT   METALLIC 

EXTERNAL   CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

IV.—  VERY  HARD. 

128 

Tourmaline 

In  all 

Resinous  to 

H.=7 

Usually  in    separate    crys- 

colors. 

vitreous 

Brittle 

tals  disseminated  through 

black  most 

quartz,    etc.;    number    of 

common 

sides     of     crystals     some 

multiple  of  three;   termin- 

ations low  three-sided  pyr- 

amids ;     aggregations    of 

crystals  often  coarse  col- 

umnar;   faces  of   crystals 

deeply  striated.      G.=3  to 

3-2 

129 

Andalusite 

White  to 

Vitreous  to 

H.=6  107.5 

Orthorhombic,      often      in 

gray,  red, 

dull, 

Brittle 

square  prisms  transparent 

yellow, 

earthy 

to  opaque.     G.  =  3.i  to  3.2 

green, 

brown 

. 

130 

Beryl 

Green  to 

Vitreous; 

H.=7-5 

Sometimes    massive;     usu- 

yellowish 

yellow 

Brittle 

ally    in    separate    crystals 

and  bluish 

varieties 

(hexagonal),       terminated 

green, 

sometimes 

by     plane     bases;      faces 

white  to 

resinous 

often      striated;      usually 

light  yel- 

shows   cleavage     parallel 

low,  some- 

to base  when  broken.     G. 

times  blue 

=  2.7 

and  red 

I31 

Spinel 

Black,  red, 

Vitreous 

H.=7-7  to  8 

Isometric;  usually  in  octa- 

gray, 

Brittle 

hedrons       and      rounded 

yellow, 

grains,      transparent      to 

green, 

opaque.      G.  =3.  5  to  4.  1 

blue 

132 

Topaz 

Pale  yel- 

Vitreous to 

H.=8 

In     right    rhombic    prsims 

low,  white, 

adaman- 

Brittle 

usually  differently   modi-i 

blue,  red, 

tine 

fied    at    the    two   extrem- 

i 

and  green 

ities.     G.=3-4  to  3.66 

133 

Chrysoberyl 

Various 

Vitreous 

H.=8.5 

Orthorhombic;  transparent 

shades  of 

Brittle 

to  translucent.    G.=3-5  to 

green  to 

3-85 

yellow 

•  . 

134 

Corundum 

Blue,  red, 

Adaman- 

H.=9 

(Sapphire, 

white, 

tine  to 

Brittle  to 

Rough  hexagonal  crystals, 

ruby) 

gray,  yel- 

vitreous 

tough 

massive  to  fine  granular, 

low,  green, 

transparent      to     opaque. 

and  brown 

G.  —  3.9  to  4.1 

135 


LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Composition. 

Action  of  Acids. 

Effects  of  Heating. 

128 

Complex 
silicate 

No  action 

Dark  varieties    are  fusible 
with  difficulty;    and  after 
fusion      decomposed      by 
HaSO45  others  infusible 

I29 
130 

Silicate  of 
aluminum 

No  action 

Infusible 
Infusible 

Beryllium, 
aluminum 
silicate 

No  action 

131 

Aluminate  of 
magnesium 

No  action 

Infusible 

132 

Aluminum 
silicate  with 
silicon 
fluoride 

No  action 

Infusible 

133 

Aluminate  of 
beryllium 

No  action 

With      borax      fuses 
great  difficulty 

with 

^34 

Al,03 

No  action 

Infusible 

136 


C.— MINERALS   WITHOUT    METALLIC 

EXTERNAL    CHARACTERISTICS. 


No. 

Species. 

Color. 

Luster. 

Hardness  and 
Tenacity. 

Remarks. 

IV.— VERY  HARD. 


135 

Diamond 

White  or 

Adaman- 

H. =  io 

Isometric  ;     commonly     in 

colorless, 

tine, 

Brittle 

octahedrons;    usually 

sometimes 

greasy, 

transparent,      translucent 

pale 

brilliant 

to      opaque;      conchoidal 

shades  of 

fracture.         G.  =3.516    to 

yellow, 

3-525 

red, 

orange, 

green, 

blue, 

brown,  and 

occasion- 

ally black 

.     137 
LUSTER;   STREAK   WHITE   OR   LIGHT   GRAY. 


No. 

Composition. 

Action  of 

Acids. 

Effects  of 

Heating. 

135    Pure  carbon      No  action 


At  temperature  of  electric 
arc  in  air  burns  to  CO2; 
out  of  air  changes  to  a 
sort  of  coke 


PART   II. 
THE    COMMON    ROCKS.       - 

The  term  rock  is  applied  to  the  more  extensive  mineral 
masses  which  make  up  the  earth's  crust.  Some  of  these 
constituent  masses  are  composed  of  a  single  mineral,  but 
most  rocks  are  mineral  aggregates.  Pure  limestone  or  pure 
siliceous  sandstone  are  examples  of  rocks  consisting  of  a 
single  mineral;  the  first  is  composed  of  calcium  carbonate 
and  the  second  of  silica.  Nearly  all  rocks,  however,  are 
mineral  aggregates,  being  composed  of  two  or  more  min- 
erals ;  even  those  composed  essentially  of  a  single  mineral 
usually  contain  small  quantities  of  other  minerals.  The  term 
rock  is  ordinarily  held  to  imply  a  solid,  hard  mass,  but  in 
geological  usage  it  is  not  so  restricted,  but  is  equally  ap- 
plicable to  soft  clay,  loose  sand,  and  hard  granite. 

Although  there  have  been  distinguished  and  more  or  less 
fully  described  about  nine  hundred  distinct  mineral  species, 
a  small  number  of  these  make  up  the  great  mass  of  the 
earth's  crust :  only  about  twenty  species  are  of  prime  im- 
portance as  rock  constituents ;  these  are  the  essential  constit- 
uents of  the  rocks ;  all  other  species  are  accessory  or  acci- 
dental minerals. 

CONSTITUENTS   OF   ROCKS. 

The  principal  rock-making  minerals  may  be  included 
under  two  general  heads,  siliceous  and  calcareous  minerals. 
The  first  includes  silica  and  the  silicates  ;  the  second  the  car- 
bonates, sulphates,  and  phosphates  of  calcium. 

The  principal  rock-making  minerals  are : 

SILICA,  quartz,  the  most  abundant  mineral  of  the  earth's 
•crust. 

139 


140 


THE   COMMON  ROCKS. 


THE 
SILICATES. 


CALCA- 
REOUS 
MINERALS. 


rp,        f  Monoclinic,  —  Orthoclase. 
Feld    \  Triclinic—   (  Albite,  Oligoclase,  Ande- 
spart      KSSS2,  °rthlte'  Labr" 


Feldspath-  (  Nepheline. 
old        <  Leucite.    • 
group.      (  Analcite. 
The  Micas,  —  Biotite,  Muscovite,  and   Hydrous 

Mica.  r  . 

Amphibole  group. 
Pyroxene  group. 
Talc. 

Serpentine. 
Chlorite. 

f  Calcite  and  Aragonite. 
I  Dolomite. 
1  Gypsum. 
[Apatite. 


In  addition  to  these  most  abundant  rock-making  species, 
the  metallic  ores,  coal,  peat,  salt,  and  a  few  other  minerals 
form  limited,  but,  from  an  economical  point  of  view,  most 
important  rock  deposits.  The  metallic  ores  and  coal  have 
been  already  described  as  minerals. 


THE   CLASSIFICATION -OF   ROCKS. 

The  classification  of  rocks  can  be  based  upon  their  phys- 
ical condition  and  texture,  as  crystalline  and  uncrystalline ; 
upon  their  mineral  characters,  as  calcareous  aud siliceous  ;  upon 
their  mode  of  origin,  as  igneous  and  sedimentary;  upon  their 
structure  and  texture,  as  stratified  and  unstratified ;  upon 
whether  transformed  from  original  condition,  as  metamorphic 
or  not. 

A  classification  from  any  single  point  of  view  is  unsatis- 
factory, because  it  fails  to  display  important  relationships 
among  rocks  and  fails  to  give  much  desirable  information. 
in  regard  to  the  characters  and  properties  of  rocks. 

For  the  purposes  of  the  general  student  the  most  useful 
and  instructive  arrangement  must  involve  to  a  certain 
degree  all  of  the  above  distinctions.  While,  therefore,  none 


SEDIMENTARY  ROCKS.  141 

of  these  distinctions  are  ignored,  the  fundamental  divisions 
here  observed  are  geological  and  depend  upon  structure, 
mode  of  origin,  and  transformation. 

GENERAL   CLASSES. 

The  three  most  general  classes  under  this  arrangement 
are  : 

I.  Sedimentary  or  stratified  rocks. 
II.  Igneous  or  unstratified  rocks. 
III.  Metamorphic  rocks. 

The  sedimentary  rocks  appear  far  more  extensively  at 
the  surface  of  the  earth,  and  as  a  rule  their  constituents 
have  simpler  composition  than  those  of  the  other  classes; 
they  will  be  first  described. 


I.  SEDIMENTARY    ROCKS. 

The  sedimentary  rocks  have  resulted  from  the  deposition 
of  sediments  or  comminuted  material,  the  material  being 
primarily  derived  from  the  decomposition  and  disintegra- 
tion of  pre-existing  rocks.  The  rocks  are  therefore  deriv- 
ative or  secondary.  The  sedimentary  rocks  have  been 
generally  deposited  from  water,  and  one  of  their  most 
obvious  and  common  characteristics  is  stratification.  So 
common  is  this  origin  and  structure  that  the  terms  aqueous, 
stratified,  and  sedimentary  are  frequently  used  synony- 
mously. 

All  the  sedimentary  rocks,  however,  have  not  been  laid 
down  under  water;  very  limited  masses  have  been  accumu- 
lated on  land  :  this  fact  gives  rise  to  two  divisions  of  the 
sedimentary  rocks  : 

A.  Aqueous  ;  those  laid  down  under  water. 

B.  Terrestrially  deposited;  those  accumulated  on  land. 
It  is  true  only  in  a  very  general  sense  that  some  of  the 

aqueous  rocks  can  be  termed  stratified,  and  the  same  is  true 
to  a  greater  extent  as  regards  the  terrestrial.  It  is  evident, 
therefore,  that  the  terms  aqueous,  sedimentary,  and  stratified 
are  not  strictly  synonymous. 


142  THE    COMMON  ROCK'S. 

A.    AQUEOUS  ROCKS. 

The  aqueous  rocks  may  be  further  subdivided  into : 

(a)  Fragmental  or  mechanically  deposited. 

(b)  Chemically  deposited. 

(c)  Organic  origin. 

(a)  Fragmental  Rocks. 

The  fragmental  rocks  are  uncrystalline  and  are  usually 
either  arenaceous  or  argillaceous,  and  are  mechanically 
deposited. 

I.  Arenaceous. 

The  arenaceous,  mechanically  deposited  rocks  are  com- 
posed of  angular  or  worn  fragments  resulting  from  the  dis- 
integration and  wear  of  older  rocks.  The  principal  com- 
ponent of  the  arenaceous  rocks  is  silica,  though  small 
quantities  of  the  more  common  silicates  are  often  present,  as 
feldspar,  mica,  etc.  To  the  arenaceous  group  the  following 
varieties  belong : 

SAND. — Sand  is  comminuted  rock  material  in  an  in- 
coherent state  ;  common  sand  is  mainly  quartz-grains,  though 
some  sands  contain  fragments  of  other  minerals,  as  feldspar, 
mica,  garnet,  and  iron  oxide.  Calcareous  matter  is  also 
sometimes  present.  The  roundness  of  the  grains  of  sand 
depends  upon  the  attrition  to  which  they  have  been  sub- 
jected ;  river  and  land  sands  are  accordingly  less  likely 
to  be  round  than  those  of  sea-beaches. 

GRAVEL.— Gravel  is  composed  of  water-worn  pebbles 
which  range  in  size  from  a  pea  to  a  hen's  egg.  Various 
rock  material  may  be  present  in  the  gravel,  but,  owing  to 
its  permanence,  quartz  is  most  common.  A  gravel  beach 
usually  has  some  sand  mixed  with  the  pebbles.  The  larger 
pebbles  and  cobblestones  with  or  without  gravel  are  usually 
called  shingle. 

SANDSTONE. — Sandstone  is  a  consolidated  rock  made 
from  sand.  The  cementing  material  may  be  calcium  car- 


SEDIMENTARY  ROCKS.  14$ 

bonate,  clay,  ferric  oxide,  or  silica.  The  two  cements  last, 
named  give  the  more  durable  stone. 

Varieties  of  sandstone  are  extensively  used  as  a  building- 
stone.  It  is  quite  durable  and  is  easily  quarried  and  cut. 
The  "  brownstone  "  used  much  in  New  York  city  and  else- 
where for  building  is  quarried  in  Connecticut  and  New 
Jersey.  Sandstones  when  used  for  a  building  or  wall  should 
be  placed  with  the  bedding  horizontal,  since  that  is  the 
position  in  which  the  stone  will  stand  the  greatest  pressure 
and  absorb  the  least  moisture  from  the  foundation.  When 
pyrite  is  present  in  a  building-stone  it  is  likely  to  cause  dis- 
integration. Sandstone  is  usually  more  or  less  laminated, 
especially  if  it  contains  clay. 

When  sandstone  splits  readily  into  even  plates  or  slabs,, 
it  is  called  flagstone  or  paving-stone.  Even-grained,  friable- 
sandstones  of  various  degrees  of  fineness  are  used  as  grind- 
stones or  scythe-stones. 

NOVACULITE. — This  is  an  exceedingly  fine-grained  sand- 
stone, often  called  oilstone.  It  is  found  extensively  in 
Arkansas  and  is  valuable  for  whetstones.  Sandstones  often 
contain  a  considerable  amount  of  clay,  to  indicate  which 
they  may,  very  properly,  be  termed  argillaceous  sandstones. 

QUARTZ  CONGLOMERATE. — A  siliceous  rock  made  up  of 
sand,  pebbles,  or  angular  fragments  of  rocks  cemented 
together.  If  the  pebbles  are  rounded  the  conglomerate  is  a 
pudding-stone  ;  if  angular,  a  breccia.  The  term  " conglomerate " 
is  often  appled  to  the  pudding-stone  alone. 

GRIT. — A  grit  is  a  hard,  siliceous  conglomerate,  the 
grains  being  less  rounded  than  in  common  sandstone.  It  is 
composed  of  vitreous  quartz  and  was  formerly  sometimes 
used  for  millstones. 

2.  Argillaceous. 

CLAY. — Soft,  very  fine  grained,  almost  impalpable,  more 
or  less  plastic  material,  chiefly  kaolinite  in  composition,  and 
of  various  colors,  as  white,  gray,  yellow,  red,  brown,  or 
black.  When  wet  it  can  be  kneaded  between  the  fingers; 


144  THE    COMMON  ROCKS. 

when  dry  it  is  soft  and  friable  and  adheres  to  the  tongue. 
It  often  contains  much  quartz-sand,  and  pulverized  feldspar. 
Marl  is  a  clay  containing  carbonate  of  lime,  and  the  amount 
of  carbonate  may  be  so  large  as  to  place  the  rock  among 
the  chemically  deposited. 

SHALE. — Shale  is  a  soft,  fragile,  argillaceous  rock,  having 
an  uneven,  slaty  structure,  splitting  along  planes  parallel  to 
the  planes  of  deposit.  Gray,  brown,  black,  red,  and  other 
shades ;  consists  essentially  of  clay  with  some  fine  sand  or 
pulverized  feldspar.  It  is  fine  mud  consolidated.  Shales, 
by  the  addition  of  sand,  graduate  into  fissile  sandstones ;  by 
the  addition  of  calcareous  matter  into  limestones ;  by  the 
addition  of  carbonaceous  matter  into  coaly  shales. 

FIRE-CLAY. — A  clay  nearly  free  from  alkalies  and  iron 
and  capable  of  standing  a  great  heat  without  fusing.  It  is 
usually  of  a  light  color  and  is  found  abundantly  beneath  the 
coal  beds. 

(b)  Chemically  Deposited  Rocks. 

OOLITE. — Is  a  limestone  composed  of  minute  spherical 
grains  resembling  the  roe  of  a  fish,  each  grain  being  com- 
posed of  concentrically  deposited  layers  of  calcite.  PISO- 
LITE is  a  similar  rock  in  which  the  grains  are  as  large  as 
peas.  The  unconsolidated  oolitic  grains  are  found  as  beach 
sand  at  Pyramid  Lake,  Nev.;  similar  but  finer  sand  is  now 
forming  at  Great  Salt  Lake.  An  oolitic  rock  is  also  found 
composed  of  calcareous,  rolled  sand  cemented  by  calcium 
carbonate.  This  last  is  a  fragmental  rock.  Extensive 
deposits  of  oolitic  rock  are  known  to  exist. 

f  GYPSUM. — Is  composed  of  calcium  sulphate,  and  is  a 
chemically  deposited  rock  formed  by  the  evaporation  of  the 
water  holding  it  in  solution.  The  decomposition  is  hastened 
by  the  presence  of  an  abundance  of  common  salt  in  the  solu- 
tion. 

SALT. — Common  salt,  like  gypsum,  is  deposited  by 
evaporation  from  waters  holding  it  in  solution.  Salt  and 
gypsum  are  generally  associated,  the  latter  being  deposited 


SEDIMENTARY  ROCKS.  145 

first.  Salt  occurs  as  an  ingredient  of  other  deposits,  as  salt 
shales ;  also  in  thin  sheets  and  enormously  thick  beds. 

TRAVERTINE. — A  massive  limestone,  formed  by  deposi- 
tion from  calcareous  springs  or  streams.  It  is  usually  cel- 
lular and  more  or  less  concretionary.  A  handsome  com- 
pact, banded  kind,  translucent  and  of  great  beauty,  comes 
from  Mexico,  and  is  sometimes  called  Mexican  onyx. 

STALACTITE  AND  STALAGMITE.— These  are  deposits, 
usually  more  or  less  columnar,  formed  on  the  roofs  and  floors 
of  caves  by  deposition  from  solution. 

SILICEOUS  SINTER. — Is  composed  of  opal  silica.  Occurs 
in  compact,  porous,  and  concretionary  forms.  It  is  deposited 
from  hot  siliceous  waters,  and  is  thus  frequently  found 
around  geysers,  forming  mounds  and  occasionally  terraces. 
From  this  fact  it  is  sometimes  called  GEYSERITE.  The  .de- 
posit is  mainly  due  to  the  evaporation  of  the  water,  but  in 
some  cases  to  the  action  of  algae. 

CHERT,  FLINT. — A  dark,  compact  rock  occurring  in 
nodules  and  in  beds  and  composed  almost  entirely  of  chal- 
cedonic  quartz.  Its  mode  of  origin  is  not  thoroughly  under- 
stood. Under  the  microscope  the  siliceous  spicules  of 
sponges  and  siliceous  shells  of  diatoms,  also  calcareous  shells 
or  spines  converted  into  silica,  have  been  observed  in  it. 
The  first  two  facts  would  indicate  that  the  rock  is,  in  part 
at  least,  formed  from  the  segregated  remains  of  organisms, 
while  the  last  indicates  a  substitution  of  silica  by  a  chemical 
process.  The  mass  of  the  rock  is  believed  to  come  more 
properly  under  Chemical  Deposits,  though  in  some  cases  it 
might  be  placed  among  those  .organically  formed.  The 
nodules  occur  abundantly  in  chalk  formations. 

BUHRSTONE. — Is  a  highly  siliceous,  compact,  though  cel- 
lular rock.  It  is  principally  found  in  the  Tertiary  rocks  of 
the  Paris  basin,  and  occurs  in  beds  associated  with  sand  and 
argillaceous  marl  deposits.  The  rock  often  abounds  in  land 
and  fresh-water  shells  as  well  as  in  the  stems  and  seeds  of 
land  and  aquatic  plants,  all  converted  into  silica.  The  exact 
mode  of  deposition  is  not  known,  but  it  was  probably  the 
action  of  siliceous  waters  on  a  previously  existing  fossilifer- 


146  THE    COMMON  ROCKS. 

ous  rock,  the  silica  replacing  other  material.  The  rock  is 
chalcedonic  quartz  and  is  largely  used  for  millstones  in 
flouring-mills,  cement-factories,  potteries,  chemical  works, 
and  other  similar  establishments.  It  has  also  been  found  in 
the  Tertiary  of  South  Carolina. 

MARL. — Marl  is  a  clay  containing  a  greater  or  less  pro- 
portion of  CaCO3 ,  from  a  small  per  cent  to  over  one-half. 
Though  testacea  are  usually  abundant  in  marl  beds,  the 
CaCO3  has  more  generally  been  deposited  from  waters 
holding  it  in  solution ;  to  this  extent  marl  is  a  chemically 
deposited  rock.  When  the  clay  is  taken  into  consideration 
marl  might  be  classed,  as  already  stated,  as  an  argillaceous 
sedimentary  rock.  The  marls  are  used  as  fertilizers. 


(c)  Organic  Origin. 

The  rocks  of  organic  origin  are  those  mainly  composed: 
of  the  remains  of  organisms.  These  remains  have  in  many 
cases  been  acted  upon,  and  to  a  certain  extent  the  rocks 
formed  by  mechanical  agencies,  so  that  some  of  them  might 
properly  be  classed  as  mechanically  deposited  rocks,  but 
their  essential  origin  rather  than  their  accumulation  is  their 
more  distinctive  characteristic. 

LIMESTONE. — This  is  a  general  term  which  includes  all 
those  rocks  mainly  composed  of  CaCO8,  though  they  vary 
greatly  in  degree  of  purity. 

Most  limestones  are  of  organic  origin  and  are  marine 
deposits,  though,  as  already  seen,  some  are  chemically  de- 
posited by  streams  or  springs.  The  organic  limestones 
show  every  gradation  of  structure  and  texture.  The  de- 
posits range  from  thin  laminae  to  beds  several  thousand  feet 
in  thickness.  In  some  the  organic  remains  are  shown  in 
almost  perfect  preservation,  in  others  the  organic  origin  is 
only  evident  under  the  microscope,  and  in  still  others  the 
organic  structure  is  no  longer  visible.  From  formations 
now  being  made  in  coral  regions  it  is  known  that  rocks  of 
evident  organic  origin  do  not  always  show  this  origin  in. 


SEDIMENTARY  ROCKS.  147 

their  texture  ;  oome  of  the  more  important  and  distinctive 
organic  limestones  are  the  following : 

SHELL-MARL. — This  is  a  friable  rock  mainly  composed  of 
shells  and  their  fragments  cemented  together  by  calcium 
carbonate.  Clay  and  sand  are  usually  present.  Such  de- 
posits are  generally  formed  in  lakes  and  ponds.  When  com- 
pacted into  solid  stone  they  constitute  fresh-water  lime- 
stones. 

COQUINA. — Shell-limestone.  Coquina  is  a  marine,  porous 
shell-limestone  made  up  almost  entirely  of  fragments  of 
shells,  though  occasional  shells  are  entire.  When  first  re- 
moved from  the  ground  the  rock  is  soft  and  may  be  easily 
cut;  by  exposure  to  the  air  it  is  greatly  hardened.  This 
rock  is  found  in  Florida  and  is  extensively  used  in  the  forts 
and  structures  of  St.  Augustine.  In  the  Florida  rock  the 
spaces  between  the  shells  are  often  partially  filled  with  clear 
quartz  sand.  The  stone  is  now  being  formed  at  numerous 
points  along  the  Florida  coast.  Shell-limestones  are  formed 
at  other  places,  but  they  differ  from  coquina  in  that  they 
are  more  compacted  ;  such  a  rock  is  found  along  the  Genesee 
river,  near  Rochester,  N.  Y. 

CHALK. — Is  a  white  earthy,  friable  limestone,  composed 
mainly  of  the  shells  and  shell-remains  of  rhizopods. 

HYDRAULIC  LIMESTONE. — This  is  an  impure  limestone 
containing  clay  and  which,  when  calcined,  yields  a  lime 
which  furnishes  hydraulic  cement ;  that  is,  a  cement  which 
sets  under  water.  The  indications  of  hydraulic  properties 
in  a  limestone  are  compact  texture,  argillaceous  odor,  con 
choidal  fracture,  and  sluggish  effervescence. 

DOLOMITE. — Is  not  distinguished  by  the  eye  alone  from 
calcite  limestone.  It  is  calcium-magnesium  limestone  and 
occurs  in  beds  often  associated  with  gypsum  and  rock  salt, 
also  in  irregular  bands  traversing  limestone.  The  origin  of 
dolomite  is  not  fully  understood.  In  some  cases  it  seems  to 
have  been  deposited  as  calcium  carbonate  and  subsequently 
a  portion  of  the  calcium  carbonate  was  replaced  by  magne- 
sium carbonate,  by  the  chemical  action  of  the  magnesium 
salts  in  sea- water. 


148  THE    COMMON  ROCKS. 

In  other  instances  this  action  seems  highly  improbable, 
and  the  rock  was  more  likely  formed  as  suggested  by  Hunt, 
being  deposited  in  closed  oceanic  basins  whose  waters  were 
rich  in  magnesium  carbonate.  Dolomite  contains  less  than 
fifty  per  cent  of  magnesium  carbonate,  the  remainder  being 
calcium  carbonate.  Sing  Sing  marble,  a  typical  dolomite, 
gives  an  hydraulic  lime  by  cautious  reduction,  reducing 
the  MgCO3  with  perhaps  some  of  the  CaCO,.  Reduction  at 
high  temperature  gives  a  fat  lime. 

CALCAREOUS  CONGLOMERATE. — A  rock  composed  of 
fragments  of  calcite  or  dolomite  cemented  by  calcium  car- 
bonate. If  the  pebbles  are  rounded  the  conglomerate  is  a 
pudding-stone ;  if  angular,  a  breccia.  The  term  "  conglomerate" 
is  often  applied  to  the  pudding-stone  alone. 

Other  massive  limestones  are  often  named  from  the  char- 
acter of  the  predominating  organic  remains — such  are  coral 
rock,  which  consists  of  fragments  of  coral  and  other  marine 
remains  cemented  by  CaCO3 ;  crinoidal  limestone  is  composed 
largely  of  the  disks  and  stems  of  crinoids  cemented  together  ; 
mummulitic  limestone  is  a  cream-colored  rock  consisting  of 
nummulites,  little  flattened,  disk-shaped  fossils,  cemented  by 
calcite.  Some  of  the  pyramids  of  Egypt,  including  that  of 
Cheops,  are  made  of  this  rock. 

GREENSAND. — An  olive-green  sand-rock,  friable,  con- 
sisting mainly  of  grains  of  glauconite  (hydrous  silicate  of 
aluminum,  iron,  and  potassium)  with  more  or  less  sand. 
Many  of  the  glauconite  grains,  under  the  microscope,  are 
seen  to  be  the  casts  of  foraminiferous  shells,  and  the  proba- 
bilities seem  to  be  that  the  glauconite  was  originally  de- 
posited in  organisms. 

SILICEOUS  LIMESTONE. — A  limestone  containing  sili- 
ceous sand.  It  has  a  gritty  feel  under  the  fingers  and  may 
be  distinguished  by  dissolving  the  pulverized  rock  in  hy- 
drochloric acid,  when  the  sand  will  be  left  as  a  gritty 
powder  which  is  capable  of  scratching  glass. 

MARBLE. — Any  limestone  which  occurs  in  large  masses 
and  is  capable  of  receiving  a  polish  is  included  under  the 
-general  term  marble ;  a  more  restricted  use  confines  it  to 


SEDIMENTARY  ROCKS.  149 

the  metamorphic,  crystalline  limestones.  If  the  marble  has 
colors  distributed  in  blotches  or  streaks  it  is  called  varie- 
gated ;  if  it  contains  angular  fragments  it  is  called  brecciated 
marble.  Many  of  the  calcareous  rocks  referred  to  give 
marbles. 

TRIPOLITE. — An  infusorial  earth,  consisting  chiefly  of 
siliceous  shells  of  diatoms  with  the  spicules  of  sponges,  and 
is  silica  in  the  opal  state.  It  resembles  clay  or  impure 
chalk  in  appearance,  but  is  a  little  harsh  between  the 
fingers  and  scratches  glass  when  rubbed  on  it.  It  forms 
thick  deposits,  and  is  often  found  in  old  swamps  beneath 
the  peat.  It  derives  its  name  from  Tripoli  in  Africa,  where 
it  was  first  obtained. 

CARBONACEOUS  DEPOSITS. — Peat  and  the  various  forms 
of  coal  come  under  this  head,  all  being  of  vegetable  origin. 
Peat  is  a  mass  of  partially  disintegrated  and  decomposed 
vegetable  matter.  It  has  a  black  or  brown  color  and  is 
much  richer  in  carbon  than  unchanged  vegetable  matter. 
In  recent  peat,  or  that  in  which  the  carbonization  has  not 
greatly  progressed,  the  vegetable  structure  is  readily  de- 
tected by  the  unaided  eye,  but  in  the  more  perfect  forms  it 
can  only  be  seen  by  the  microscope.  It  occurs  in  many 
places  and  is  valuable  as  a  fuel.  The  various  forms  of  coal 
have  been  already  referred  to  as  minerals. 

B.    TERRESTRIAL  OR  LAND-FORMED  ROCKS.* 

This  division  includes  the  rocks  accumulated  on  land 
or  areas  not  habitually  covered  by  water.  ,Such  rocks  are 
principally  produced  and  accumulated  by  meteoric  agen- 
cies. The  most  important  of  this  class  is  the  soil. 

SOIL. — This  is  a  general  term  for  the  products  which 
result  from  the  subaerial  decomposition  and  disintegration 
of  the  more  compacted  rocks  of  the  earth's  surface.  It  is 

*  There  is  no  general  agreement  in  the  classification  of  the  rocks  here 
included  under  the  term  terrestrial.  Nearly  the  same  formations  have 
been  included  under  the  terms  aerial,  subaerial,  and  ceolian,  but  none  of.' 
these  is  thought  to  be  as  appropriately  applicable  as  that  adopted. 


15°  THE    COMMON  ROCKS. 

an  intimate  mixture  of  such  material  and  generally  contains 
some  animal  and  vegetable  matter.  The  mineral  matter  of 
the  soil  often  results  from  the  rocks  immediately  below  it, 
but  it  may  be  more  or  less  transported.  All  fertile  soils 
contain  organic  matter. 

ALLUVIUM. — Is  a  term  applied  to  the  soil  brought  to 
gether  by  the  ordinary  operations  of  water,  especially 
during  times  of  flood.  It  generally  constitutes  the  flats  on 
either  side  of  streams  and  is  usually  in  layers  varying  in 
fineness,  due  to  successive  depositions. 

BLOWN  SANDS. — Loose  sands,  of  whatever  origin,  may 
be  blown  into  mounds  or  heaps,  forming  dunes  or  downs, 
and  if  they  be  calcareous  sands  or  contain  considerable  cal- 
careous matter,  they  may  by  the  action  of  rain-waters  be 
converted  into  compact  stone. 

LOESS. — Is  a  term  applied  to  certain  widely  distributed 
deposits  which  have  the  same  general  characteristics,  but 
probably  all  have  not  been  deposited  in  the  same  way. 
The  material  under  consideration  is  a  light-colored  loamy 
earth,  generally  unstratified.  It  covers  immense  areas  in 
northern  China,  in  the  pampas  of  South  America,  and 
occurs  as  extensive  bluff-deposits  along  the  Mississippi  and 
its  tributaries,  along  the  Rhine,  Danube,  and  other  Euro- 
pean rivers.  Somewhat  similar  deposits  occur  in  the  basin 
regions  of  our  western  country.  The  origin  of  these  for- 
mations is  not  yet  solved.  In  some  regions  they  have  been 
ascribed  to  the  action  of  the  wind,  which  is  known  to  have 
deposited  immense  quantities  of  dust  after  carrying  it 
through  great  distances.  In  certain  arid  regions  dust- 
storms  have  been  known  to  fill  the  atmosphere  with  dust 
for  days,  even  obscuring  the  sun.  Wind-blown  dust  is 
probably  one  of  the  sources  of  loess  deposit ;  another  is 
thought  to  be  rain-washed  sediment  from  bare  slopes.  The 
loess  of  river-valleys  generally  was  probably  laid  down  in 
water  during  the  periods  of  flooded  lakes  and  rivers. 

GUANO. — This  substance  is  a  mixture  of  organic  matter^ 
ammonium  salts  and  phosphate,  of  lime.  It  is  a  brown,  light, 
porous  body  with  an  ammoniacal  odor.  The  deposits  of 


SEDIMENTARY  ROCKS.  !$! 

guano  occur  in  rainless  regions  and  are  the  droppings  of  the 
immense  flocks  of  sea-fowl  that  have  for  centuries  frequented 
the  regions.  South  America  and  the  rainless  islands  off  the 
western  coast  of  that  continent  contain  the  most  noted  de- 
posits. If  the  underlying  rock  is  calcium  carbonate  it  may 
be  gradually  converted  into  calcium  phosphate.  Similar 
•deposits  made  by  bats  have  been  found  in  many  caves. 

VOLCANIC  TUFA  is  a  rock  formed  from  the  comminuted 
fragmentary  material  ejected  from  volcanoes.  These  mate- 
rials are  consolidated  partly  by  pressure  and  partly  by  infil- 
trating waters.  Vast  quantities  of  fine  matter  are  often 
ejected  from  volcanoes,  the  finest  being  termed  ashes.  There 
is  a  gradation  from  this  through  sand  into  the  coarser  vari- 
eties of  ejected  matter.  The  term  "  ash  "  is  used  because  of 
its  resemblance  to  the  ash  from  wood  or  coal,  but  no  result 
of  combustion  is  implied.  The  tufas,  or  "  tuffs  "  as  the  word 
is  sometimes  written,  include  the  rocks  formed  from  the 
consolidated  ashes,  sand,  and  finer  material. 

The  ejected  material  may  fall  into  bodies  of  water,  thus 
giving  aqueous  as  well  as  terrestrial  tufas.  The  finer  ejected 
material,  especially  that  of  a  sandy  nature,  is  sometimes 
called  peperino.  The  erupted  matter  from  volcanoes  and 
fissures  forms  other  extensive  land  deposits,  but  thev  cannot 
be  included  under  the  head  of  sedimentary  rocks. 

TALUS. — This  is  a  term  applied  to  the  piles  of  earth  and 
bowlders  generally  seen  at  the  base  of  cliffs  and  mountain- 
slopes.  Talus  results  from  the  unceasing  action  of  gravity 
and  meteoric  agencies  in  dragging  down  the  higher  eleva- 
tions. In  the  case  of  cliffs,  if  the  debris  is  not  removed  from 
the  base,  the  precipice  will  in  time  be  converted  into  a 
slope. 

DETRITUS. — Detritus  is  the  general  term  for  earth,  sand, 
alluvium,*  silt,  gravel,  and  mud.  The  material  is  derived  to 

*  The  alluvial  material  is  constantly  carried  into  lakes,  bays,  etc.,  at 
the  mouths  of  the  rivers  and  streams.  It  is  not  under  such  circumstances  a 
terrestrial  deposit.  In  bays  and  harbors  these  shore  deposits  are  usually 
called  silt.  They  tend  to  delta  formation  and  may  eventually  give  rich 
alluvial  lands. 


I  $2  THE    CO  MAI  ON  ROCKS. 

a  great  extent  from  the  wear  of  rocks  through  disintegrating 
agencies,  attrition  and  decomposition. 

DRIFT. — Drift  is  the  unstratified  sand,  gravel;  and  stones, 
with  more  or  less  clay,  deposited  by  glaciers ;  it  is  also  called 
TILL. 


II.  IGNEOUS    OR   UNSTRATIFIED    ROCKS. 

The  first  of  these  terms  is  applied  to  this  class  of  rocks 
because  heat  has  evidently  been  concerned  in  their  origin, 
and  the  second  because  of  the  entire  absence  of  true  strati- 
fication. These  rocks  are  believed  to  have  consolidated  from 
a  fused  or  semi-fused  condition.  The  term  eruptive  is  some- 
times used  as  synonymous  with  the  above  terms,  but  eruptive 
is  also  used  as  the  equivalent  of  volcanic,  and  will  be  so 
understood  in  this  text. 

EVIDENCE  OF  ORIGIN. — The  igneous  origin  of  these  rocks 
is  primarily  involved  in  the  accepted  theory  of  the  earth's 
origin,  and  they  are  believed  to  have  been  the  rocks  first 
formed  and  to  have  resulted  from  the  cooling  and  solidifica- 
tion of  the  molten  globe  ;  they  are  therefore  the  primitive 
rocks  from  which  all  others  have  been  derived  and  must  of 
necessity,  at  greater  depths,  underlie  all  superficial  rocks. 
Subsequently  and  up  to  the  present  time  all  exposed  igneous 
rocks  have  been  produced  from  within  the  earth's  crust,  and 
there  is  the  strongest  ground  for  thinking  that  all  have  been 
in  a  molten  or  a  pasty  condition.  The  effects  which  the 
igneous  rocks  have  frequently  produced  upon  the  sedimen- 
tary deposits  with  which  they  have  come  in  contact,  and  the 
extreme  similarity  of  these  rocks,  in  many  cases,  to  modern 
lavas,  leave  little  doubt  that  heat  has  been  an  agent  in  their 
production. 

CHARACTERISTICS  OF  IGNEOUS  ROCKS. — The  igneous 
rocks  in  general  differ  from  the  sedimentary  by  the  absence  of 
all  lamination,  due  to  the  sorting  of  material ;  by  the  texture, 
which  is  more  or  less  crystalline,  glassy,  or  compact ;  by  the 
absence  of  fossils,  and  by  the  marked  difference  in  the, 
manner  of  occurrence. 


IGNEOUS   OR    UNSTRATIFIED    ROCKS.  153; 

Besides  the  general  terms  of  coarse  and  fine  texture, 
descriptive  of  rocks,  the  igneous  rocks  display  four  distinct 
types  of  texture  with  gradations  from  one  to  the  other. 
These  types  are  designated  as  follows : 

ist.  Glassy,  in  which  the  rock  is  a  glass  mixture,  not 
showing  distinct  minerals ;  is  devoid  of  crystalline  masses  and 
has  that  texture  which  is  best  described  by  the  term  itself 
and  thus  universally  recognized.  The  incipient  stages  of 
crystallization  are  often  shown  under  the  microscope  in 
native  glasses,  by  hair-like  formations  (trichites)  and  minute 
grains  (spherulites).  When  the  fused  glass  material  is  sub- 
jected to  the  action  of  escaping  gases,  there  may  be  pro- 
duced a  fine  cellular  or  vesicular  mass,  thus  giving  rise  to. 
pumiceous  or  scoriaceous  texture. 

2d.  Compact,  in  which  the  mass  is  made  up  of  minute 
crystals  too  small  to  be  seen  by  the  eye  alone.  When  the 
microscope  reveals  the  crystals  the  rock  is  macrocrystalline, 
and  when  they  cannot  thus  be  seen,  cryptocrystalline.  Compact 
rocks  are  homogeneous  and  stony,  not  glassy  in  appearance. 

3d.  Porphyritic,  in  which  distinct  crystals  are  inter- 
spersed throughout  a  ground  mass  which  is  glassy,  minutely 
crystalline,  or  both.  The  large  crystals  are  called  pheno- 
crysts.  This  texture  is  thought  to  indicate  two  periods  of 
crystallization,  the  phenocrysts  forming  first  and  the  magma 
solidifying  later.  In  some  cases,  if  not  all,  the  phenocrysts 
were  formed  before  the  rock  was  erupted  and  hence  are 
said  to  be  intratelluric. 

4th.  Granitoid,  in  which  the  texture  is  wholly  crystalline 
without  any  amorphous  ground-mass. 

CLASSIFICATION    OF    IGNEOUS    ROCKS. 

The  igneous  rocks  for  the  purposes  of  the  general 
student  can  be  best  and  most  significantly  divided  into  two 
primary  groups,  plutonic  and  volcanic,  with  a  less  distinctly 
defined  group  forming  an  intermediate  series.  The  typical 
members  of  the  first  two  groups  are  distinctly  different, 
but  other  members  of  the  group  approach  each  other 
by  insensible  gradations  until  they  might  with  equal 


154  THE   COMMON  ROCKS. 

propriety  be  assigned  to  either ;  these  form  the  intermediate 
series  and  are  sometimes  classed  as  intrusive  rocks.  These 
divisions  of  the  igneous  rocks  involve  distinctions  both  in 
mode  of  occurrence  and  in  the  texture  of  the  kinds. 

i.  Plutonic  Rocks. 

The  plutonic  rocks  occur  in  the  greater  masses  and  have 
cooled  and  solidified  at  greater  depths  than  the  other  groups 
and  consequently  more  slowly.  They  have  never  been 
erupted  on  the  surface.  This  slow  cooling  has  led  to  a  more 
perfect  and  wholly  crystalline  texture.  They  have  the 
granitoid  texture;  that  is,  the  rocks  are  made  up  of  an 
aggregate  of  crystals  more  or  less  perfect  without  any  un- 
crystallized  ground-mass  between  the  crystals.  They  are 
coarsely  crystalline  (macrocrystalline)  and  granular.  The 
constitutent  minerals  are  mainly  quartz,  the  feldspars,  mica, 
and  hornblende.  The  principal  rocks  of  this  group  are  : 

GRANITE. — Common  granite  consists  of  quartz,  feldspar, 
and  mica.  Massive,  with  no  appearance  of  layers  in  the 
arrangement  of  the  mineral  ingredients.  G.  =  2.5  to  2.8. 
The  quartz  usually  transparent,  bluish  glassy,  without 
cleavage ;  the  feldspar  (usually  orthoclase)  opaque  white  or 
reddish  with  glistening  cleavage  surface ;  the  mica  in  glisten- 
ing scales,  either  whitish  or  black.  When  all  the  crystals 
are  small  and  the  rock  evenly  granular  it  is  sometimes 
called  eurite  or  granulite.  When  the  feldspar  is  in  well- 
defined  crystals  in  a  finer  but  still  crystalline  ground-mass, 
it  is  called  porphyritic  granite.  When  the  rock  also  contains 
hornblende  it  is  called  syenitic  granite.  When  the  mica  is 
replaced  by  hornblende  it  is  called  hornblende  granite. 
Granite  is  generally  plutonic,  but  sometimes  metamorphic. 

PEGMATITE  (Graphic  Granite]  consists  mainly  of  quartz 
and  feldspar  with  little  or  no  mica  or  hornblende,  the 
quartz  existing  as  bent  plates  in  the  feldspar,  giving  in 
cross-section  the  appearance  of  Hebrew  or  Arabic  charac- 
ters. 

SYENITE   is  a   rock  composed  essentially  of  orthoclase 


IGNEOUS   OR    UNSTRATIFIED    ROCKS.  155 

and  hornblende.  The  hornblende  may  be  replaced  by 
biotite  or  augite,  giving  mica  or  augite  syenite. 

The  term  syenite  has  been,  in  many  places,  used  to 
describe  the  rock  above  referred  to  as  hornblende  granite. 
It  still  has  a  wide  popular  use  in  this  sense  in  this  country. 

DIORITE. — A  dark,  speckled,  greenish  or  grayish  black 
rock,  generally  consisting  of  a  crystalline  aggregate  of 
triclinic  feldspar  (oligoclase)  and  hornblende,  though  some 
varieties  contain  pyroxene  or  biotite.  Quartz  frequently 
present ;  if  in  large  quantity  it  makes  quartz-diorite.  Usu- 
ally granitoid  in  texture,  though  much  finer  than  granite. 
Generally  plutonic,  sometimes  metamorphic. 

DIABASE. — A  dark,  greenish,  crystalline  rock,  similar  in 
appearance  to  diorite,  but  containing  augite  in  place  of 
hornblende.  Usually  fine-grained.  Often  contains  olivine. 

GABBRO. — A  coarse-grained  variety  of  diabase. 

The  above  selections  include  the  more  typical  rocks  of 
the  plutonic  group,  but  they  graduate  into  each  other  and 
give  rise  to  many  varieties. 

Diorite  and  diabase  are  often  intrusive,  and  accordingly 
fall  also  in  the  intermediate  series  of  trappean  rocks. 

2.  Eruptive  or  Volcanic  Rocks. 

The  volcanic  rocks  have  been  brought  to  or  near  the 
surface  by  volcanic  action  and  thus  have  been  subjected  to 
more  rapid  cooling  than  the  plutonics.  This  has  generally 
resulted  in  a  wholly  glassy  or  only  a  partially  crystalline 
texture ;  when  partially  crystalline,  the  crystals  are  im- 
bedded in  an  amorphous  or  glassy  paste  ;  they  are  usually 
micro-  or  cryptocrystalline,  and  have  a  minutely  speckled 
appearance.  While  generally  the  characters  are  as  stated 
above,  some  of  the  volcanics  are  holocrystalline,  but  even 
then  the  principal  mass  of  the  rock  is  likely  to  be  of  very 
minute  crystals.  The  difference  in  texture  between  the 
volcanic  and  plutonic  rocks  is  due  to  their  modes  of  oc- 
currence, which  involves  difference  in  the  conditions  of 
cooling. 

OBSIDIAN. — Lava  which  has  been  completely  fused  and 


156  THE   COMMON  ROCKS. 

cooled  rapidly.  A  volcanic  glass.  Gray  to  black.  Breaks 
with  a  conchoidal  fracture,  the  splinters  often  transparent. 
Most  of  the  obsidians  are  essentially  composed  of  ortho- 
clase.  Its  dark  color  and  opacity  are  due  to  vast  numbers 
of  incipient  crystals. 

Pitchstone  has  much  the  appearance  of  obsidian,  but 
contains  water. 

PUMICE. — A  finely  vesicular,  light-colored  variety  of 
scoria.  It  is  so  light  that  it  will  float  upon  water.  A 
strikingly  similar  substance  can  be  produced  by  injecting 
steam  into  certain  iron  slags.  Pumice  may  result  from 
different  magmas,  but  the  more  common  kind  is  composed 
essentially  of  orthoclase.  It  is  often  capillary  or  in  thread- 
like masses,  even  silky. 

RHYOLITE. — This  is  one  of  the  most  common  kinds  of 
lava  erupted  when  the  original  igneous  material  is  granitic 
in  composition.  The  ground-mass  is  mainly  orthoclase  in 
minute  crystals  with  more  or  less  glass.  It  has  the  por- 
phyritic  texture,  the  isolated  crystals  (phenocrysts)  being 
of  quartz  and  sanidin.  Rhyolites  are  exceedingly  abundant 
in  the  western  United  States.  When  coarsely  granular  it 
is  sometimes  called  nevadite.  Liparite  and  quartz  trachyte 
are  also  names  applied  to  forms  of  rhyolite. 

TRACHYTE. — A  light-colored,  ash-gray  rock.  It  consists 
of  a  ground-mass  which  is  mainly  minute  orthoclase  crys- 
tals, with  little  or  no  glass,  with  phenocrysts  of  sanidin  of 
glassy  luster.  Often  contains  amphibole,  pyroxene,  or  bio- 
tite,  and  is  slightly  porphyritic  in  texture.  It  graduates 
into  rholite. 

PHONOLITE. — A  compact,  grayish-blue  or  brown  feld- 
spathic  rock,  somewhat  slaty  in  structure.  It  clinks  under 
the  hammer.  It  differs  in  composition  from  trachyte  in 
containing  nepheline  and  sometimes  leucite  and  horn- 
blende. It  is  a  rare  rock  in  this  country. 

BASALT. — This  term  is  applied  to  many  varieties  of  the 
volcanic  rocks,  which  differ  considerably  in  appearance. 
As  most  commonly  applied  it  is  a  dark,  almost  black, 
cryptocrystalline  rock,  breaking  with  a  dull,  slightly  con- 


IGNEOUS   OR    UNSTRATIFIED    ROCKS.  1 57 

choidal  fracture.  It  contains  microscopic  crystals  of  labra- 
dorite,  augite,  and  usually  olivine,  in  a  ground-mass  of  the 
same.  Magnetite  is  often  an  abundant  constituent. 

DOLERITE,  has  the  same  composition  as  basalt,  except 
the  olivine,  and  is  more  coarsely  crystalline.  Its  color  is 
dark  grayish.  It  is  commonly  called  trap-rock,  a  term 
which  is  applied  to  several  other  granular  volcanic  rocks. 

ANDESITE. — A  dark-grayish  rock,  consisting  essentially 
of  triclinic  feldspar  (oligoclase  or  andesite),  with  horn- 
blende (or  augite). 

3.  Intermediate,  Intrusive  Rocks. 

In  the  plutonic  and  volcanic  groups  we  have  described 
only  the  more  typical  varieties,  but  there  are  many  other 
igneous  rocks  which  cannot  with  more  distinctness  be 
assigned  to  one  rather  than  to  the  other  of  these  groups. 
Many  of  these  ill-defined  rocks,  in  their  mode  of  occurrence 
as  well  as  their  texture,  are  intermediate  between  the  plu- 
tonic and  the  volcanic.  The  volcanic  are  generally  the 
superficial  igneous  rocks  ;  the  plutonic  are  the  profound 
masses  underlying  the  surface ;  the  intermediate  series 
form  the  connecting  conduits  and  sheets  between  them. 
Sometimes  they  are  driven  like  wedges  between  the  strata 
which  rest  upon  the  plutonics  and  are  overlaid  by  the 
volcanics.  The  most  common  of  the  intermediate  rocks  are 
intrusive  forms  of  dolerite,  diorite,  and  diabase.  They 
differ  from  the  plutonic  varieties  only  in  their  modes  of 
occurrence,  which  may  also  affect  their  texture.  The 
terms  trap  and  greenstone  are  often  applied  to  the  basaltic 
intrusive  rocks. 

FELSTTE  is  a  light-colored  intrusive  rock,  usually  red- 
dish or  gray.  It  is  compact,  fine-grained,  and  composed 
chiefly  of  feldspar  and  quartz  without  glass.  It  is  often 
porphyritic  in  texture,  the  phenocrysts  being  of  quartz  or 
feldspar.  The  first  is  sometimes  called  quarts-porphyry,  and 
the  second  porphyrite.  The  term  porphyry  is  applicable  to 
any  rock  which  consists  of  a  homogeneous  base,  with  well- 
defined  crystals  of  the  same  material  or  another  mineral. 


158 


THE    COMMON  ROCKS. 


We  thus  often  have  greenstone  porphyry  as  well  as  felsitic 
porphyry.  The  term  porphyry  is  very  generally  employed 
by  miners  in  our  West  for  any  rock  that  occurs  in  what 
they  call  veins. 


OTHER   MODES   OF   CLASSIFICATION   OF  IGNEOUS   ROCKS. 

No  single  common  system  for  the  classification  of 
igneous  rocks  has  been  adopted.  In  addition  to  the  divi- 
sions based  upon  their  mode  of  occurrence,  above  given, 
other  divisions,  based  upon  chemical  and  mineralogical  com- 
position, are  very  generally  recognized,  and  are  more  fun- 
damental to  the  special  student.  This  method  of  classifying 
gives  the  following  groups  for  the  rocks  described: 

i(i)  f  Obsidian.      ")  The     principal    minerals 

j  Pitchstone.          present  are  orthoclase 
Granite-rhyo-  J  Pumice.  and   quartz,   oligoclase 

lite  family.      ,  Rhyolite.       {       in    subordinate    quan- 
|  Felsites.  tity,  with    some   horn- 

(_  Granites.       J       blende  and  mica. 

Principal  minerals  pres- 
ent are  orthoclase  and 
hornblende,  some  oli- 
goclase, pyroxene,  and 
biotite.  Quartz  gener- 
ally absent;  orthoclase 
predominating  mineral' 

-syenite  belongs  to  this 
nepheline  and  leucite 

replacing  orthoclase. 

"]  Plagioclase  (soda-lime) 
feldspar  is  the  predomi- 
nating mineral,  with 
hornblende  in  consider- 
able quantity.  Pyrox- 
ene and  biotite  may 
occur.  Quartz  in  small 
quantity. 

Principal   minerals  pres- 
ent,    plagioclase    feld- 
spar     (labradorite      or 
}•      anorthite)    and    pyrox- 

Iene.  Magnetite  and 
olivine  are  often  pres- 
ent. 


(2) 

' 

S  y  enite-tra- 
chytefamily. 

- 

Trachyte. 
Phonolite. 
Syenite. 

j 

I  n  t  e  r  media  t  e 
group,  contain- 
ing      between  - 
55   and  65   per 
cent  of  silica. 

(3) 

Nephelit< 
family, 
largely 

1 

Diorite-Ande- 
site  family. 

Andesite. 
Diorite. 

(4) 


Basic  group,  con- 
taining    be- 
tween  45   and  • 
55  per  cent  of 
silica. 

Basalt-Gab-  ^ 
bro  family. 

Basalt. 
Dolorite. 
Diabase. 
Gabbro. 

Ultra-Basic, con- 
taining gener- 
ally less  than 
45  per  cent  of 

silica. 


(5) 


Rocks  composed  almost  entirely  of  pyroxene  or  horn- 
blende and  olivine. 

Serpentine  rocks. 


METAMORPHIC  ROCKS.  159 


III.   METAMORPHIC   ROCKS. 

The  metamorphic  rocks  are  those  which  have  been 
produced  by  the  transformation  without  disintegration  of 
pre-existing  rocks.  This  transformation  generally  involves 
one  or  more  and  often  all  the  following  changes — greater 
hardness,  different  and  more  crystalline  texture,  develop- 
ment of  different  minerals.* 

One  of  the  most  important  characteristics  of  many  of  the 
metamorphic  rocks  is  a  foliated  structure.  This  term  gener- 
ally refers  to  that  structure  brought  about  by  the  presence 
of  minute  scales,  such  as  produce  the  fissile  character  of 
schists,  but  the  term  is  now  often  used  in  a  more  general 
sense  and  is  made  to  include  cleavage. 

Until  quite  recently  it  was  thought  that  metamorphic 
rocks  were  all  originally  sedimentary  rocks,  but  it  is  now 
known  that  the  original  rocks  often  belonged  to  the  igneous 
classes.  Metamorphic  rocks  may  be  said  to  have  had  two 
dates,  one  of  formation  and  one  of  transformation. 

The  metamorphic  rocks  have  great  extent  and  thickness 
at  many  places  throughout  the  world.  The  more  important 
kinds  are  the  gneisses,  schists,  clay  slate,  marbles,  quartzite, 
and  serpentine.  The  gneisses,  schists,  and  slates  have  the 
foliated  structure,  the  other  kinds  have  not.  The  foliation 
in  slates  is  usually  termed  cleavage. 

COMMON  GNEISS. — This  rock  has  the  general  appearance 
and  mineral  composition  of  granite,  but  the  ingredients  are 
arranged  in  layers.  Gneiss  grades  insensibly  on  the  one 
hand  into  granite  and  on  the  other  through  the  schists  into 
sandy  clays  or  clayey  sands.  It  is  now  thought  that  gneiss 
has  frequently  resulted  from  the  metamorphism  of  granite. 

If  hornblende  is  also  present  as  a  constituent  in  the  rock 
it  becomes  syenitic  gneiss. 

*The  term  metamorphic  has  recently  been  used  to  include  rocks  altered 
by  decomposition  and  disintegration.  Such  use  greatly  enlarges  this  class 
of  rocks,  but  also  makes  the  use  of  the  term  very  general  and  less  definite. 


l6o  THE    COMMON  ROCKS. 

THE  SCHISTS. — More  or  less  fissile  rocks,  made  up  largely 
of  scales  or  thin  crystals  of  the  minerals  from  which  they 
derive  their  names.  The  structure  is  called  schistose,  and 
differs  entirely  from  that  of  slates. 

The  structure  is  included  under  the  general  term  of  folia- 
tion. It  is  now  thought  that  schists  may  have  been  derived 
either  from  igneous  or  sedimentary  rocks. 

The  varieties  of  schists  are : 

Mica  Schist. — This  is  a  grayish  fissile  rock  consisting  of 
mica,  considerable  quartz,  and  frequently  some  feldspar.  It 
often  contains  garnets.  Some  varieties  are  used  for  flag- 
stones. 

Hydromica  Schist. — Composed  chiefly  of  hydrous  mica  or 
of  this  with  some  quartz.  The  surface  nearly  smooth,  pearly 
to  faintly  glistening  in  luster,  grayish  in  color. 

Chlorite  Schist. — Grayish  green,  smooth  but  not  greasy  to 
the  feel.  Consists  of  chlorite  with  usually  some  quartz  and 
feldspar.  Often  contains  crystals  of  magnetite. 

Talcose  Schist. — Composed  essentially  of  talc.  Has  the 
appearance  and  feel  of  talc. 

Hornblende  Schist. — Schistose,  dark-colored,  rough  to 
the  feel,  composed  of  hornblende. 

CLAY  SLATE  (ARGILLITE). — An  argillaceous  rock,  split- 
ting into  thin  even  slabs,  the  planes  of  cleavage  running 
athwart  the  stratification  planes.  Many  of  the  common 
slates  contain  considerable  quantities  of  mica  and  hydro- 
mica  in  scales.  They  are  generally  derived  from  sediment- 
ary argillaceous  rocks,  but  it  is  believed  that  they  may 
result  through  the  transformation  of  volcanic  tufas. 

THE  MARBLES. — The  marbles  were  originally  common 
limestone,  but  metamorphism  has  produced  in  them  a  crys- 
talline-granular texture.  They  are  either  calcite,  dolomite, 
or  calcite-dolomite.  They  often  contain  mica,  tremolite, 
talc,  pyroxene  or  apatite.  Some  of  the  common  marbles 
are: 

Statuary  Marble. — Pure  white  and  fine  grained. 

Architectural  Marble  is  coarse  or  fine  grained,  white 
and  mottled  of  various  colors. 


METAMORPHIC  ROCKS.  l6l 

Verd  Antique,  Ophiolite. — A  marble  containing  serpentine. 

QUARTZITE  is  a  changed  siliceous  sandstone,  usually 
firm  and  hard.  The  grains  and  the  cement  holding  them 
together  are  both  silica.  It  generally  requires  the  micro- 
scope to  recognize  the  fragmental  nature  of  the  rock,  but 
sandstones  and  quartzites  graduate  into  each  other. 

ITACOLUMITE  is  a  schistose  quartzite  through  which 
are  distributed  scales  of  mica,  chlorite,  and  talc.  The  rock 
is  often  only  slightly  compacted  and  almost  friable.  It  is 
sometimes  the  matrix  in  which  diamonds  are  found  in  Brazil. 
It  is  slightly  flexible,  due  to  the  schistose  scales. 

SERPENTINE  ROCK  is  composed  of  serpentine.  Fine 
granular,  easily  scratched  with  a  knife.  Generally  of  a  dark 
oil-green  color  and  slightly  greasy  on  a  smooth  surface. 
The  massive  compact  varieties  which  receive  a  good  polish 
are  termed  serpentine  marbles.  The  origin  of  serpentine  is 
not  well  understood  ;  in  some  cases  it  appears  to  be  derived 
from  magnesian  clays,  but  perhaps  more  often  by  the  altera- 
tion of  chrysolitic,  augitic,  and  hornblendic  rock. 


INDEX  TO  TABLES. 


Table  A — Minerals  with  metallic  luster 98-106 

41       B —        "         without"  "    ,  streak  colored 106-118 

C—        "  "        "  "    ,       "       white  or  light  gray    118-136 


Actinolite,  126 

Albite.  130 

Amphibole,  (Actinolite)  126,  (Basal- 
tic hornblende)  no,  114,  (Horn- 
blende), 106,  118,  128,  (Tremolite) 
126 

Analcite,  126 

Andalusite,  134 

Anglesite,  122 

Anhydrite,  122 

Anthracite  coal,  106 

Apatite,  128 

Aragonite,  124 

Argentite,  102,  104 

Arsenopyrite,  (Mispickel)  100 

Augite,  108,  116,  130 

Azurite,  118 

Basaltic  hornblende,  no,  114 
Beryl,  134 
Biotite,  122 
Bituminous  coal,  106 
Bornite,  98 
Bronzite,  128 

Calamine,  126 

Calcite,  118,  122;  (Chalk)  120,  (Rock 

milk)  118 
Carnallite,  122 


Cassiterite,  98,  106,  no 

Cerargyrite  (Horn-silver),  120 

Cerussite,  124 

Chalcedonic  quartz,  132 

Chalcocite,  102,  104 

Chalcopyrite,  98 

Chalk,  120;  red,  114 

Chlorite,  116,  122 

Chromite,  104 

Chrysoberyl,  134 

Chrysocolla,  116,  118,  124 

Chrysolite,  132 

Cinnabar,  no,  114 

Coal  Anthracite,   106;    Bituminous, 

106 

Copper,  98 

Corundum  (Sapphire,  Ruby),  134 
Crocidolite,  116 
Cryolite,  122 
Cuprite,  98,  108,  112 

Diallage,  126 
Diamond,  136 
Dolomite,  124 

Enstatite,  128 
Erubescite,  98 


Fluorite,  124 
Franklinite,  104,  108 


163 


1 64 


INDEX   TO    TABLES. 


Galenite,  IO2 

Garnet,  132 

Gold,  98 

Graphite,  100,  102,  106 

Gypsum,  120 

Halite,  122 

Hematite,    (Specular  iron   ore)  102, 

104,  112,  (Red  chalk)  no 
Hornblende,  106,  no,  114,  118,  128 
Horn-silver,  120 
Hypersthene,  128 

Jasper,  132 
Kaolinite,  120 

Lapis  Lazuli,  118 
Leucite,  130 
Lignite,  108 

Limonite,    no,   114,   (Yellow  ocher) 
112,  lib 

Magnetite,  104,  108 

Malachite,  116 

Malacolite,  130 

Melaconite,  104,  106 

Mica,  (Muscovite)  120,  (Biotite)  122 

Microcline,  132 

Mispickel,  100 

Molybdenite,  100 

Monazite,  128 

Muscovite,  120 

Nephelite,  130 
Niter,  120 

Ocher,  yellow,  112 
Olivine  (Chrysolite),  132 
Opal,  130 
Orthoclase,  130 


Proustite,  98,  112 

Pyrargyrite,  104,  112 

Pyrite,  100 

Pyrolusite,  104 

Pyroxene,    (Augite)   108,    116,    130,, 

(Diallage)  126,  (Malacolite)  130 
Pyrrhotite,  100 

Quartz  (Vitreous,  Chalcedonic,  Jas- 
pery),  132 

Red  chalk,  no 

Ruby,  134 

Rutile,  98,  106,  no,  132 

Sapphire,  134 
Serpentine,  116,  124 
Siderite,  114,  126 
Silver,  100 
Smithsonite,  126 
Specular  iron  ore,  102 
Sphalerite,  108,  114,  124 
Spinel,  134 
Stephanite,  104 
Stibnite,  100 
Sulphur,  112,  120 

Talc,  120 
Tennantite,  102 
Tenorite,  106 
Tetrahedrite,  102 
Topaz,  134 
Tourmaline,  134 
Tremolite,  126 
Turquois,  130 

Willemite,  128 
Witherite,  124 

Zincite,  114 


GENERAL  INDEX. 


PACK 

Actinolite • 82 

Adularia • .  •  • 87 

Agate,  common 75 

fortification 75 

,  moss 76 

Alabaster 68 

Albite 87 

Alexandrite 65 

Alluvium 150 

Almandine,  almandite 84 

Amethyst 75 

Amianthus 82 

Amphibole 81 

group . 80 

Amphigene 88 

Analcime,  analcite 89 

Andalusite 90 

Andesite 88,  157 

Angles,  constancy  of 10 

,  interfacial 2 

,  plane,  solid 2 

Anglesite 50 

Anhydrite 69 

Anorthite 88 

Antimony,  glance 60 

,  gray  ...... 60 

Anthracite . 94 

Apatite . . . 69 

Aquamarine 84 

Argentite,  silver  glance 40 

Argillite 160 

Arragonite 72- 

165 


166  GENERAL   INDEX. 

PACK 

Arsenopyrite 55 

Asbestu  s 82 

Asbestus,  ligniform 82 

Augite 80 

Aventurine .  75 

Axes,  crystallographic 6 

of  symmetry 3 

,  principal 17 

Azurite 48 

Basalt 156 

Bauxite 63 

Beauxite 63 

Beryl 83 

Biotite 86 

Bituminous  coal 95 

Black  copper  ore 46 

silver  ore,  stephanite 41 

Blende,  zinc 51 

Bloodstone 76 

Blown  sand 150 

Blowpipe  test  for  iron,  lead,  zinc 30 

,  use  of 29 

Bog-iron  ore 58 

Bornite 44 

Bort 32 

Breccia 143 

Brittleness,  property  of 26 

Bronzite 81 

Buhrstone 76,  145 

Cairngorm 75 

Calamine 52 

Calcite 70 

Calcium,  compounds  of 67 

phosphate 69. 

sulphate,  hydrous 69 

Calcspar : 70 

Carbonaceous  deposits 149 

Carbonates 32 

Carbuncle 85 

Carnallite 67 

Carnelian 76 

Cassiterife 61 

*"at's  eye,  chrysoberyl 65 

quartz 75 


GENERAL   INDEX.  l6/ 

PACK 

Cerargyrite,  horn-silver • 41 

Cerussite 50 

Chalcedony 75 

Chalcocite 45 

Chalcopyrite 45 

Chalk . 71,  147 

,  French 92 

Chalybite 59 

Chemical  properties  of  minerals 27 

Charcoal,  use  of 28 

Chert 145 

Chlorite. '«. 94 

Chloropfcane 67 

Chromite Bo 

Chrysoberyl » 64 

Chrysocolla 48 

Chrysolite 83, 

Chrysoprase 76 

Chrysotile 93 

Cinnabar 42: 

Cinnamon-stone 84 

Clay,  common 90,  143, 

,  fire 144 

Cleavage 8,  9 

Coal,  anthracite 94 

,  bituminous 96 

Coal,  brown 95 

,  cannel 95 

,  mineral 94 

Colophonite 84 

Color  of  minerals 25 

Columnar  structure 23 

Concretions ' 24 

Conglomerate,  calcareous 148 

,  quartz 143 

Copper,  common,  test  for 44 

glance 45 

,  native,  occurrence  of 43 

ores 44 

pyrites 45 

,  variegated 46 

,  vitreous 45 

Corundum 62 

Coquina 14? 

Crocidolite 82 

Cryolite 66 


168  GENERAL   INDEX. 

PAGE 

Crystalline  aggregates 23 

systems. i ! 

Crystallography,  geometric .,.. 2 

,  physical 2 

Crystals,  definition I 

,  relating  to 8 

,  distortion  in 19 

,  multiple 20 

,  parallel  grouping 20 

,  twins,  contact,  penetration 21 

Cuprite 46 

Dendritic  structure 23 

Detritus 151 

Diabase . • 155 

Diallage 80 

Diamond 32 

,  source  of 33 

Diaspore 63 

Diorite 155 

Distortions  in  crystals 19 

Dog-tooth  spar 72 

Dolerite 157 

Dolomite 73,  147 

Downs 150 

Drift 151 

Drusy  surface 23 

Dunes 150 

Edge,  beveled 9 

,  replaced 9 

.     ,  truncated 9 

Edges I 

Electro-silicon 78 

Emerald 83 

Emery 63 

Enstatite :, 81 

Erubescite. 46 

Essonite 84 

Eurite 154 

Faces 1,9 

,  curved,  striated 20 

Feldspar 86,  87 

,  common,  potash 87 

,  soda > 87 


GENERAL   INDEX.  169 

PAGE 

Telsite 157 

Felspathoid  group 88 

Fibrous  structure 23 

Fiorite 77 

Flagstone , 143 

Flexibility,  property  of 26 

Flint 76,  145 

Fluorite 67 

Fluorspar 67 

Fluxes , 30 

Foliated  structure 158 

Forceps,  use  of 28 

Forests,  petrified 76 

Forms,  clinometric 6 

,  closed,  open 18 

,  fundamental 8 

,  holohedral,  hemihedral 19 

,  orthometric 6 

,  unit 8 

Franklinite 58 

Gabbro 155 

Galena 50 

Galenite 50 

Garnet , 84 

,  precious i- 84 

Geodes 24 

Geyserite 77,  145 

Glauconite 148 

Gneiss,  common , 159 

,  syenitic .._•  •  • .*. 159 

Gold,  method  of  obtaining 37 

,  native ...  • . 36 

,  occurrence  of 36 

,  production  in  U.  S 38 

Granite 154 

,  graphic , 154 

,  hornblendic 155 

,  porphyritic 154 

,  syenitic 154 

Granular  structure 23 

Granulite 154 

Graphite 33 

Gravel 142 

Gravity,  specific » 26 

'Gray  antimony. 66 


GENERAL   INDEX. 

PACK 

Gray  copper  ore 46 

Greensand ' 148 

Greenstone,  trap 157 

Grindstones 143 

Grit * 143 

Guano 150 

Gypsum 68,  144 

Halite....* 65, 

Hammer,  and  anvil,  use  of 28 

Hardness  table  of 26 

Heliotrope 76 

Hematite,  brown 58 

,  red 56 

Hemihedral 19, 

Holohedral \ 19 

Hornblende 83, 

Horn-silver,  cerargyrite 41 

Hypersthene 81 

Ice-stone 66 

Iceland  spar 72 

Indices,  rationality  of 9, 

Indicolite 92 

Infusorial  earth 79 

Iron  carbonate 59 

,  native 53 

,  ores  of 54 

Pyrites 54 

Isomorphism 21 

Itacolumite 161 

Jasper 76 

Jet....- 95 

Kaolinite 90 

Labradorite 88 

Lamellar  structure 23 

Lapis  lazuli. 85 

Law  of  axial  ratios ;  gfr 

Lead  carbonate 50 

,  ores  of 49 

sulphate 50 

sulphide 49 

Lepidolite 86, 


GENERAL  INDEX. 


Leucite 88 

Lewis,  H.  C 33 

Limestone,  chemically  deposited 71 

,  crinoidal 148 

,  hydraulic 147 

,  lithographic 71 

,  nummulitic 148 

,  oolitic 71 

,  origin  organic 146 

,  siliceous 148 

Limonite 58 

Liparite 156 

Lithographic  limestone 71 

Loess I5a 

Magnesium  limestone 73 

Magnetic  pyrites 55 

Magnetite 57 

Malachite 47 

Malacolite 80 

Malleability,  property  of 26 

Manganese,  black  oxide  of 60 

Marble 148,  160 

,  architectural 160 

,  brecciated 149 

,  serpentine 161 

,  statuary 160 

,  variegated 149 

Marl 146 

,  shell- 147 

Martite 57 

Melaconite 47 

Mica 85 

,  uses  of 86 

Microline 88 

Milky  quartz ; ...  75 

Mineralogy,  chemical 2 

,  crystallographic 2 

,  definition i 

,  descriptive , 3 

Mineral  species I 

Minerals,  definition I 

Mispickel 55 

Monazite 64 

Mortar,  steel , 28 

,  agate 4 28 


1/2  GENERAL   INDEX. 

PAGE 

Moss-agate  ....».••*»»••• , 76 

Mountain  leather , , • 82 

Multiple  crystals , 20 

Mundic. 56 

Muscovite 86 

Nepheline,  nephelite. 89 

Niter * 66 

Novaculite 143 

Obsidian 155 

Ocherous  ore,  iron .. 58 

Odors  of  minerals 26 

Oilstone -. » • 143 

Oligoclase 89 

OH  vine * 83 

Onyx *. 76 

Oolite 144 

Oolitic  limestone , 71 

Opal ,...,, , 77 

Opalescence... ...... ,.,..,., ....... 25 

Ophiolite ... ., 93,  161 

Orthoclase 87 

Parallel  grouping 20 

Parameters,  rationality  of 9 

Paving-stones , , 143 

Peat , , 149 

Pegmatite , 154 

Peperino ... 151 

Peridot 83 

Phonolite ,. 156 

Phosphorescence , 25 

Physical  properties  of  minerals,. 25 

Plagioclase •  •  .,..• t . . .  .  88 

Planes,  like , 9 

,  location  by  axes 7 

,  similar... , 9 

Platinum,  native. , .,.,.. 38 

Play  of  colors  , , 25 

Plumbago 33 

Porphyrite 157,  158 

Porphyry,  quartz- 15^ 

Proustite,  red  silver  ore ^ 41 

Pseudomorphs 21 

Pudding-stone. ., ... ..,..,. 143 


GENERAL   INDEX.  I  7$ 

PAGE 

Pumice 156 

Pyrargyrite,  ruby  silver • . .  40 

Pyrites,  iron.. . . 54 

Pyrolusite 61 

Py  rope 84 

Pyroxene  division . . 79 

group 80 

Pyrrhotite 55 

Quartz 74 

,  chalcedonic  series 75 

,  crystalline  series 74 

,  granular 76 

Quartzite 161 

Reagents 30 

Red  copper  ore 46 

Rhyolite 156 

Rock  crystal 74 

-forming  minerals. 139,  140 

milk 72 

Rocks,  aqueous 142 

,  chemically  deposited 144 

,  classification  of 140 

Rock  salt * 65 

Rocks,  common 139 

,  constituents  of ; 139 

,  eruptive ^ .  * , 155 

,  general  classes  of 141 

,  igneous,  classification  of •. 153 

,  characteristics  of . . . .  i. 152,  153 

,  origin  of. ; < 152 

,  unstratified < ***«.»• 152 

,  intermediate ;....* *...  157 

r  intrusive « « -.  • 157 

,  land-formed • .  * 149 

,  metamorphic 159 

organic  in  origin 146 

,  plutonic < * 154 

,  sedimentary 141 

,  tabular  classification  of... 157 

,  volcanic f 155 

Rose  quartz ...*........ 75 

Rubellite •. 92 

Rubies,  Arizona. ................  4 85 

Ruby,  common  ...;;*.....-....  *  ..«.-.<..•« * 66 


174  GENERAL   INDEX, 

PAGE 

Ruby,  oriental 63 

Ruby  silver,  pyrargyrite 40 

Rutile 62 

Salt,  common  rock 66,  144 

Saltpeter 66 

Sand 142 

Sands,  blown 149 

Sandstone ' 142 

,  flexible,  itacolumite 161 

Sanidin 87 

Sapphire 63 

Sard 76 

Sardonyx 76 

Satin  spar,  calcite 72 

,  gypsum * .  68 

Schists 160 

chlorite 160 

hornblende 160 

hydromica 160 

mica 1 60 

talcose 160 

Scythestone 143 

Sectility,  property  of 26 

Selenite 68 

Serpentine,  precious,  common 93 

rock 161 

Shale 144 

Siderite 59 

Silica 74,  139 

Silicates,  classification  of 78 

Siliceous  sinter 77 

Silver  glance,  argentite 40 

Silver,  native 39 

,  ores  of , 40 

,  sources  of 41 

Slate,  clay 160 

Smithsonite 52 

Smoky  quartz 75 

Soapstone 92 

Soil 149 

Spathic  iron  ore 59 

Specific  gravity 26 

Specular  iron  ore 56 

Sphalerite 51 

Spinel 64 


GENERAL   INDEX.  1/5 

PAGE 

Stalactites 71,  I4g 

Stalactitic  structure 24 

Stalagmites ylt  I45 

Steatite 92 

Stephanite,  black  silver  ore 41 

Stibnite 60 

Stratified  structure 24 

Streak  of  minerals.. . . . 25 

Sulphur,  native ^4 

,  sources  of 35 

Syenite I55 

Symmetry,  axes  of 3 

,  center  of 4 

,  crystallographic 3 

,  elements  of 3 

,  planes  of 3,  17 

Systems,  crystalline,  isometric n 

,  monoclinic 15 

,  orthorhombic ..... 14 

,  tetragonal,  hexagonal 12 

,  triclinic 5 

Tables,  description  of  use 96 

Talc 92 

,  indurated 92 

Talus 151 

Tennantite < 46 

Tests,  miscellaneous •. < 31 

Tetrahedrite 45 

Till 152 

Tin  ore,  black 61 

oxide 61 

stone • 61 

Topaz 89 

Tourmaline 91 

Trachyte   156 

,  quartz 156 

Trap-rock 157 

Travertine 71,  145 

Tremolite 82 

Tridymite 77 

Tripolite 77 

Tubes,  closed 29 

,  test  with 31 

,  open 29 

,  test  with 30 


176  GENERAL   INDEX. 

PAGE: 

Tufa,  calcareous 71 

,  volcanic ;.. 151 

Turquois 63 

Ultramarine 85 

Verd-antique v 93i  161 

White  lead  ore 5° 

Willemite 52 

Wire,  platinum,  use  of 29 

Witherite 74 

Zinc  blende 53 

carbonate 53 

,  ores  of 5i 

silicate 52 

Zincite 52 

Zonal  relations » Jo 

Zone • 10 


X/ 


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Treatise  on  Belts  and  Pulleys 12mo,  1  50 

Dana's   Text-book   of  Elementary   Mechanics   for    the    Use   of 

Colleges  and  Schools 12ma,  1  50 

Dingey's  Machinery  Pattern  Making 12mo,  2  00 

Dredge's  Record  of  the  Transportation  Exhibits  Building  of  the 

World's  Columbian  Exposition  of  1893 4to,  half  mor.,  5  00 

Du  Bois's  Elementary  Principles  of  Mechanics: 

Vol.  I.— Kinematics  Svo,  3  50 

Vol.  II.— Statics 8vo,  4  00 

Vol.  III.— Kinetics Svo,  3  50 

Du  Bois's  Mechanics  of  Engineering.    Vol.  I Small  4to,  10  00 

Durley's  Elementary  Text-book  of  the  Kinematics  of  Machines. 

(In  preparation.) 

Fitzgerald's  Boston  Machinist 16mo,  1  00 

Flather's  Dynamometers,  and  the  Measurement  of  Power.  12mo,  3  00 

"        Rope    Driving 12mo,  2  00 

Hall's  Car  Lubrication 12mo,  1  00 

Holly's  Art  of  Saw  Filing 18mo,  *     75 

*  Johnson's  Theoretical  Mechanics 12mo,  3  00 

Jones's  Machine  Design: 

Part  I — Kinematics  of  Machinery Svo,  1  50 

Part  II. — Form,  Strength  and  Proportions  of  Parts.  ..  .Svo,  3  00 
Kerr's  Power  and  Power  Transmission.    (In  preparation.) 

Lanza's   Applied  Mechanics Svo,  7  50 

MacCord's  Kinematics;   or,  Practical  Mechanism Svo,  5  00 

"          Velocity  Diagrams Svo,  1  50 

Merriman's  Text-book  on  the  Mechanics  of  Materials Svo,  4  00 

*  Michie's  Elements  of  Analytical  Mechanics Svo,  4  00 

Reagan's  Locomotive  Mechanism  and  Engineering 12mo,  2  00 

Reid's  Course  in  Mechanical  Drawing Svo,  2  00 

"       Text-book    of    Mechanical     Drawing    and    Elementary 

Machine   Design Svo,  3  00 

Richards's  Compressed  Air 12mo,  1  50 

Robinson's  Principles  of  Mechanism Svo,  3  00 

Sinclair's  Locomotive-engine  Running  and  Management.  .12mo,  2  00 

Smith's  Press- working  of  Metals Svo,  3  00 

Thurston's   Treatise   on  Friction   and   Lost  Work   in  Machin- 
ery and  Mill  Work Svo,  3  00 

Animal  as  a  Machine  and  Prime  Motor,  and   the 

Laws  of  Energetics 12mo,  1  00 

Warren's  Elements  of  Machine  Construction  and  Drawing.  .Svo,  7  50 
Weisbach's     Kinematics     and     the     Power    of     Transmission. 

(Herrman— Klein.)    Svo,  5  00 

"  Machinery  of  Transmission  and  Governors.     (Herr- 

(man— Klein.)    Svo,  5  00 

Wood's  Elements  of  Analytical  Mechanics Svo,  3  00 

"       Principles  of  Elementary  Mechanics 12mo,  1  25 

"       Turbines   Svo,  2  50 

The  World's  Columbian  Exposition  of  1893 4to,  1  00 

14 


METALLURGY. 

Idlest on's  Metallurgy  of  Silver,  Gold,  and  Mercury: 

Vol.  I —Silver 8vo,  7  50 

Vol.  II.— Gold  and  Mercury 8vo,  7  50 

Keep's  Cast  Iron.     (In  preparation.) 

Kunhardt's  Practice  of  Ore  Dressing  in  Lurope 8vo,  1  50 

Le  Chatelier's  High-temperature  Measurements.     (Boudouard — 

Burgess.)  12mo,  3  00 

Metcalf's  Steel.     A  Manual  for  Steel-users 12mo,  2  00 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  00 

Part  II.— Iron  and  Steel 8vo,  3  50 

Part  III. — A  Treatise  on  Brasses,  Bronzes  and  Other  Alloys 

and  Their  Constituents 8vo,  2  50 

MINERALOGY. 

Barringer's    Description    of    Minerals    of    Commercial    Value. 

Oblong,  morocco,  2  50 

Boyd's   Resources  •  of    Southwest    Virginia 8vo,  3  00 

"       Map  of  Southwest  Virginia Pocket-book  form,  2  00 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.)  .8vo,  4  00 

Chester's  Catalogue  of  Minerals 8vo,  paper,  1  00 

Cloth,  1  25 

Dictionary  of  the  Names  of  Minerals 8vo,  3  50 

Dana's  System  of  Mineralogy Large  8vo,  half  leather,  12  50 

"       First  Appendix  to  Dana's  New  "  System  of  Mineralogy." 

Large  8vo,  1  00 

Text-book  ftf  Mineralogy 8vo,  4  00 

Minerals  and  How  to  Study  Them 12mo,  1  50 

Catalogue  of  American  Localities  of  Minerals .  Large  8vo,  1  00 

"      Manual  of  Mineralogy  and  Petrography 12mo,  2  00 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Hussak's     The     Determination     of     Rock-forming     Minerals. 

(Smith.)    Small  8vo,  2  00 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of 

Mineral  Tests . .  ;  8vo,  paper,  50 

Rosenbusch's  Microscopical  Physiography  of  the  Rock-making 

Minerals.      (Idding's.) .8vo,  500 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks .  .  8vo,  2  00 
Williams's  Manual  of  Lithology 8vo,  3  00 

MINING. 

Beard's  Ventilation  of  Mines 12mo,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  00 

"       Map  of  Southwest  Virginia Pocket-book  form,  2  00 

*  Drinker's     Tunneling,     Explosive     Compounds,     and     Rock 

Drills 4to,  half  morocco,  25  00 

Eissler's  Modern  High  Explosives 8vo,  4  00 

Goodyear's  Coal-mines  of  the  Western  Coast  of  the  United 

States  12mo,  250 

Ihlseng's  Manual  of  Mining 8vo,  4  00 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe 8vo,  1  50 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  00 

Sawyer's  Accidents  in  Mines 8vo,  7  00 

Walke's  Lectures  on  Explosives 8vo,  4  00 

Wilson's  Cyanide  Processes 12mo,  1  50 

Wilson's  Chlorination  Process 12mo,  1  50 

15 


Wilson's  Hydraulic  and  Placer  Mining 12uio,  2  00* 

Wilson's  Treatise  on  Practical  and  Theoretical  Mine   Ventila- 
tion  12mo,  1  25 

SANITARY  SCIENCE. 

Fol well's  Sewerage.     (Designing,  Construction  and  Maintenance.) 

8vo,  3  0(V 

Water-supply    Engineering 8vo,  4  00 

Fuertes's  Water  and  Public  Health 12mo,  1  50 

Water-filtration   Works 12mo,  2  50 

Gerhard's  Guide  to  Sanitary  House-inspection 16mo,  1  00 

Goodrich's  Economical  Disposal  of  Towns'  Refuse. .  .Demy  8vo,  3  50 

Hazen's  Filtration  of  Public  Water-supplies 8vo,  3  00 

Kiersted's  Sewage  Disposal 12mo,  1  25 

Mason's  Water-supply.     (Considered   Principally  from  a  San- 
itary Standpoint 8vo,  5  00 

"        Examination    of    Water.      (Chemical    and    Bacterio- 
logical.)  12mo,  1  25 

Merriman's  Elements  of  Sanitary  Engineering 8vo,  2  00 

Nichols's  Water-supply.     (Considered  Mainly  from  a  Chemical 

and  Sanitary  Standpoint.)     (1883.)  8vo,  2  50 

Ogden's  Sewer  Design 12mo,  2  00 

Richards's  Cost  of  Food.    A  Study  in  Dietaries 12mo,  1  OO 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sani- 
tary   Standpoint 8vo,  2  00 

Richards's  Cost  of  Living  as  Modified  by  Sanitary  Science .  12mo,  1  00 

Rideal's  Sewage  and  Bacterial  Purification  of  Sewage 8vo,  3  50- 

Turneaure  and  Russell's  Public  Water-supplies «• 8vo,  5  00 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Woodhull's  Notes  on  Military  Hygiene 16mo,  1  5Q 

MISCELLANEOUS. 

Barker's  Deep-sea  Soundings 8vo,  2  00 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Ex- 
cursion   of    the    International    Congress    of    Geologists. 

Large  8vo,  1  50 

FerreFs  Popular  Treatise  on  the  Winds 8vo,  4  00 

Haines's  American  Railway  Management 12mo,  2  50 

Mott's  Composition,  Digestibility,  and  Nutritive  Value  of  Food. 

Mounted  chart,  1  25 

"      Fallacy  of  the  Present  Theory  of  Sound 16ma,  1  00 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute,  1824- 

1894 Small    8vo,  3  00 

Rotherham's  Emphasised  New  Testament Large  8vo,  2  00 

"  Critical  Emphasised  New  Testament 12mo,  1  50 

Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

Totten's  Important  Question  in  Metrology 8vo,  2  5Q 

The  World's  Columbian  Exposition  of  1893 4to,  1  00 

Worcester  and  Atkinson.     Small  Hospitals,  Establishment  and 
Maintenance,  and  Suggestions  for  Hospital  Architecture, 

with  Plans  for  a  Small  Hospital 12mo,  1  25- 

HEBREW    AND    CHALDEE    TEXT-BOOKS. 

Green's  Grammar  of  the  Hebrew  Language 8vo,  3  00 

"       Elementary  Hebrew   Grammar 12mo,  1  25 

"       Hebrew  Chrestomathy 8vo,  2  00 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament 

Scriptures.     (Tregelles.) Small  4to,  half  morocco,  5  00 

Letteris's  Hebrew  Bible 8vo,  2  25 

16 


YC  32865 


785375 


gineering 
Library 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


